hey, "is all clear" is GOOD! well, iFLUTD (idiopathic feline urinary tract disease) are caused by bladder stones/bacterial infection in most case but sunny is all clear (does that include cystitis check too?) - so it would be from stress of enivromental change or litterbox stress -

he could be in pain for many reasons, interor swollening, bad inflammation, orlatered GAG (glycosaminoglycan) layer or leakage from blood vessels inside & more. hope you had all panel of blood works done. sometimes those symptoms wouldn't show right away.

I'm happy to hear he's a little bit himself this morning and let's hope the new treatment will work this time so he'd not have to suffer anymore!

hugs,
..gina & miles (miles hopes sunny doesn't mind his long-haired but wanted to send his love luck)