The Peter Gurney Guinea Pig Pages - Cystitis
This needs clearing up as it sounds as though it`s advanced to the stage where there are crystals or stones involved and this can sometimes mean being surgically removed. In rats, it`s called Urolithiasis, but I`m not sure the it`s the same in guinea pigs, but I can imagine it`s still as bad.
Cystitis in any pet can cause pain when urinating and also abdominal pain. I would keep a close eye on Piglet (I`m presuming Piglet is a male?) and check his penile area daily. Watch his behaviour as he urinates and check the urine for blood or whether he`s agitated when trying to pass urine.
The link I provided is from peter Gurney`s webs page. But there are so many good websites you could research on this and get the best treatment for Piglet.
His diet should have added cranberry extract or berries as cranberries have a compound that helps prevent bacteria from sticking to the bladder walls, but this would only be helpful secondary to the antibiotics you are administering. I wouldn`t worry too much about gimmicky treats and stick to good natural herbs and make sure he is well.
Has his tummy bloating went down? You may also want to look up `bloating in guinea pigs` in case this is a separate issue. x
And no, piggies shouldn`t have toilet roll tubes they are too small.