Please see a vet in the coming week during regular opening hours. Urinary tract problems generally present with very similar symptoms, so it is often an elimination process. With a urine infection (UTI), a bacterial cystitis or a sterile recurring cystitis it usually takes several days for symptoms to firm up and become constant and not off and on. Ideally you vet should palpate the bladder to see whether it is hard or soft to judge the likelihood of a stone or sludge issue being at the bottom; an x-ray will bring confirmation if there are any concerns in that direction.
If your piggy is suddenly looking very off, suddenly losing weight very quickly, off their food and increasdingly lethargic, then it is very likely that a bladder stone has been washed into the urethra and is blocking it. This is a life or death see a vet or out-of-hours vet asap emergency that you should be aware of. Otherwise, normal opening hours are perfectly fine with any urinary tract issue.
Please don't panic but seek vet care if you find more red-stained pees.