Hi! A comment on UTIs...cats often get recurring UTIs when they are not eradicated the first time (it's the same infection coming back). The infection recurs then several weeks to a couple months later, even.
You need to get on antibiotics that the C/S has indicated are effective and STAY ON THEM for at least 6-8 weeks with no break. Sounds like a long time, it is. UTIs require that kind of intensity. I would also not suggest Clavamox. It's often not strong enough to deal with a urinary tract infection. Baytril, Zeniquin, and Veraflox (my favorite) are excellent choices. They also have less likely GI upset as side effect, and they are known to be very thorough with eradicating urinary and kidney infections.
After you get off those antibiotics (after 6-8 weeks minimum), you wait 10 days then do another urinalysis (vet can look under microscope manually) to make sure the urine is cleared. Does this help? We've had a lot of UTIs in this house!
If it's idiopathic cystits, this is a moot point what I Just wrote - but I Hope it's useful information for you to have if you ever do have a UTI and need it! If it's idiopathic cystitis and you need Prednisolone, never fear there is still hope to become regulated with the FD and Pred. My rule of thumb has been to always give the Pred, b/c you can always increase insulin dose as needed.