Don't sweat it - we're all learning all the time and some vets have just a bit more piggy experience than others. There's a lot of great stuff on the internet and a lot of crazy misleading dross but we can't tell one from the other! Piggy-wise this is the forum for me - if it's not on here already you can start a thread about it and the volunteers have decades of piggy experience between them. We still can't tell what your girls are suffering from but we can suggest possibilities and things to consider. Apols for this long post btw!
First thing is that I've had a few pigs with urinary tract infection (UTI) over the years - genuine infections that have been confirmed and treated by antibiotics. And I've
never had piggies pass this type of infection onto a cage mate. It's turned up more in my girls and we think that might be because of how they scent mark by wiping their bits on the ground. That's piggy life. Some turned out to have a stone too and this has likely made it easier for the infection to hold on and cause symptoms: typically wet round the back from dripping pee, blood tint in urine, hunching and squeaking in pain while peeing. The only time I ever saw a proper puddle of blood was a little sow who seemed to have suddenly passed a stone out of nowhere (she ended up fine btw). Still tweaking our diet and doing better these days: the reduction in pellets and changing our water to low Ca seems to have made a good difference so far, touch wood!
Anyway, some of these UTIs have been more difficult to shift with the antibiotics but the pattern of reduction in symptoms has always been the same for us. We start the antibiotics and can see a difference within a day or two (48 hours). Sometimes a 5 (or 7) day course has cleared an infection no problem - we
always complete the course - but we
always see the difference in the first few days. This is a typical pattern and this is why people are very tempted not to complete courses of antibiotics because they think, "Oh it's worked already"! But we must.
On only one occasion there was no improvement after 72 hours (3 days) and I called the vet back. She said the bacteria must be resistant to that antibiotic and prescribed a different one straight away which fortunately worked - a day and a half later my girl was drying up at the back and a lot more comfortable.
One time we completed the course but a few days afterwards the symptoms came back because, presumably, not quite all the bacteria had been wiped out. The vet just prescribed the same thing again, this time for nearly 3 weeks, but we still saw the initial improvement within 48 hours. So if antibiotics are genuinely effectively treating bacteria the easing of piggy's symptoms tends to follow the same pattern. Is this the pattern you have seen? Or is it that you get, say, a 10 day course and see some improvement after several days because in this case I'd be thinking more about SIC and that the antibiotic is a coincidence
There are a few piggies on here with sterile interstitial cystitis (SIC) which is apparently also a thing in cats with stress - we met a young tom at the vet who was getting over a few weeks of difficulty with SIC after moving house. Stress is a trigger but tbh all piggies, as prey animals, must feel stress quite a lot anyway and we don't know why some get these symptoms while most others don't. You can't test for it and the symptoms are the same (or very similar) to UTI but don't respond to those treatments. It is characterised by 'flare-ups' but piggy can get through these and if you can find the right balance they can live happy lives. I mean, some people apparently get it too and vets don't offer to put
us down, or even our cats! Cat treatments include glucosamine and something called Feliway cystease has been used by piggy people too. Search the forum for it and you'll find people discussing how much they give and how... there's a nice pic somewhere of some powder made into a little sandwich with cucumber! Glucosamine does not need a prescription as it counts as a food supplement... but it's just knowing how and when to give it. People use it for other things too - bladder support after stone surgery or long term infection - not just SIC. My old boy is on it for arthritis and doing great. I'm a total convert as George is much more mobile now.
But it doesn't work like magic - it needs a few weeks to build up. In George's case he seemed to be laying around less after 2 weeks (I just thought he was a bit lazy!) but by 4 weeks he was following his females out into the kitchen which he'd not done for months. George also used to have hair in his teeth as he nibbled on his stiff joints like we rub our sore joints. That's gone now. If your girl is self-barbering she's not happy... but you know that already x
We use oxbow joint support lozenges which contain 90mg glucosamine. They also do a urinary support one but this only has 45mg per lozenge. Some pigs don't like them - mine love them. My girl with occasional gritty pee has half a George-lozenge to crunch each day. It's likely no coincidence that she takes more than her share of the pellets - she's my fattest pig despite being bottom pig. Feliway cystease comes in capsules and has to be put on the food - it seems to be well tolerated in pigs. I've seen something called 4Joints liquid (for dogs) which has been recommended too although I can't remember if that was for arthritis or bladders or both!
We can't buy Metacam/Loxicom (active ingredient meloxicam) without a prescription as it is a painkiller and anti-inflammatory but it is commonly used for piggies and George is on it for the rest of his life. They like the taste - it's not a battle to get them to take it. George runs over for his syringe and chunky Louise is always hot on his heels to try and get a lick of the empty syringe! There are 2 strengths: 0.5mg/ml for cats (now also licensed for pigs) and 1.5ml/ml for dogs (unlicensed). George -like many piggies with an experienced vet - gets dog strength although these days I have to sign a form to say I take responsibility for that. Anyone will prescribe cat strength and for some pigs that is OK but it's not really a weight for weight comparison with this stuff. George gets
about 0.25ml twice a day. I say
about because it comes with a special syringe which has it's own units. However, it's the same as you would give an 8 kilo dog - obvs George isn't
that hefty! But pigs tolerate this stuff well and have a really fast metabolism so they burn through it. My vet worked out George's dose based on mgs per kg of pig so weight is involved. She said either 8 units once a day or 4 twice. I just have to be careful not to exceed the dose per 24 hours. He has no side effects. In the short term I've had piggies on (much) higher doses with no problem but for long term arthritis management he's doing well. I hope your vet can work out a suitable regime for your sisters.
Good luck Bella and girls
I’m posting here in the hope someone may have a suggestion for a natural remedy. Lychee is a 2 year-old female Guinea pig. She’s been sick for less than a year, constant infections and bladder stones etc - we’ve had many courses of antibiotics and she keeps getting sick. We’ve tried supplements, we’ve brought her inside off the grass, different beddings, parasite treated regularly, her diet is really healthy and she drinks a lot and eats well but she’s still sick, blood all over the cage floor. The vet has x-rated her and done an ultrasound on her tummy, all he found was sludge but no big stones. Her healthy cage mate gets sick occasionally too, catches the infection off the sick one. I guess I was just wondering if there’s anything more I can try for the sick one? She’s been pulling her fur out and because she’s been sick there’s been a lot of tension and growling in the cage but if I seperate them (they’re sisters) they squeak themselves hoarse until I reunite them. The vet has broached putting her down, but I really really don’t want to do that unless it’s the only option 
Thank you in advance to any suggestions - Bella
and the vet didn’t mention a lot of this, I’ve probably been asking the wrong questions!
I’ll definitely talk to the vet about the painkillers! 
I’m so grateful to both of you, I really didn’t know what to do 
Thank you 