My thought leans toward the possibility of Lyme's disease. Tho it is not as common in cats as in dogs, they can still get it, and without even going outside. Deer ticks can be brought into your home on another animals - or on you. And the fact that kitty had a good amount of antibiotics could have kept it at bay and kept it from progressing to a deadly level. My dog Sparky had Lyme's a couple of years ago, even tho both dogs get vaccinated yearly against it. But the vaccine is only 85% effective. He had all the symptoms of Lymes with the lameness, lethargy, lack of appetite, etc, so his vet tested him for it, and the test was negative and showed he didn't have it. So a couple of weeks later after babying what we thought was a sprain or pull, he was still no better, and doc had the insight to go ahead and treat him for Lymes anyway, with the 30 day antibiotic regimen - and it worked!!! So even tho he has yearly immunizations for it, and he tested negative - he still actually had it. He's fine now, with no lingering after effects.

This could be kitty's problem - tho testing for it won't necessarily show anything, just as it didn't with Sparky. I'm hoping that I.R. Kitty~~~ that name ~~~ continues to improve.