I'm so sorry for your situation. Diarrhoea is not something we have any 'home cure' for. Is there anything he might have eaten or drank to trigger this? How long has he been bad with it?
I had one girl who I had been bathing her feet in a salt solution (something called 'Epsom salts') because she had a foot sore. Then suddenly she drank a few sips. Epsom salts is sometimes used by people as a laxative and it did give her very runny poop and gut pain but only for a day or so (it was all over the feet so it didn't help the sore). I was relieved when she started to feel better, but this happened on its own - it just had to pass through. Sometimes pigs are given antibiotics and they can upset the gut too. Sometimes they gorge on vegetables which are starting to go bad, or something else that can upset the stomach - too much fruit perhaps, which isn't good for them because of the sugar in it. It will cause pain, and they might not want to eat hay but if you can encourage them to eat a little syringe food or softened pellets just to reassure yourself that something is going in the top end to help the gut try and stabilise.
There are more serious metabolic issues that will end up in gut disturbance but the first thing to consider is could it simply have been something he has eaten. Hopefully then it might pass through his system with a little assistance. If you have no painkiller for him (such as metacam or loxicom, not a people painkiller) you could perhaps try and make a warm surface for him to lie on to ease the gut. It is cold here in the UK right now so we use heat pads, or rubber hot water bottles wrapped in a fleece or towel, butif you could just warm a rolled-up towel so he can lie on it he might get some relief. Don't bath him, but if the fur at the bottom end gets very poopy try and wipe with a damp cloth or if you have to dip his bottom in warm water (no soap) and dab it dry that is also fine. We try not to do this in the evening as it's not nice to go to bed damp!
I hope it's just temporary x
