I would say UTI. Did your vet specifically test for that?
It sounds like you KNOW the answer to the problem. Put the litter box in your bathroom and scoop it everytime there's anything in it - easy to do since you go in there to pee through out the day. Problem might be solved that simple.
|Now I know that cats can get all tied into a knot if their box is not pristine. I try to keep it clean, but if I miss a day, there wet pee all over the house.|