Welcome to Itchmo, Rebeccry... although I am saddened by the condition of your poor kitty that brought you here. You said you belonged to several yahoo feline groups. Is the CRFgroup one of those? That excellent group has a lot of very knowlegeable, helpful and compassionate people on board and if you're not a member yet, I urge you to be one!
By what you have written, I think you suspect that your cat's lack of appetite may be due to mouth/teeth problems, especially since there seems to be a corresponding betterment when you use antibiotics. Several of us here have had very good results with a new product called Biotene gel for severe mouth infections. You can try this (its not expensive) and see if it will help. I bought mine from here:http://www.healthypets.com/bioteneoralgel.html
Also, the drooling may really be becuase of a bad and aching tooth (or teeth) that ideally should be extracted. I don't know how bad your kitty's kidneys are, but perhaps you can try for a second opinion whether or not your kitty can undergo a dental under anestheia? Maybe try an all-feline vet? NedF's 18-yr old kitty had a dental about a year ago and we all remarked that NedF's vet must be a very very good one!
I'm sorry I couldn't be of more help to you since I really have had no experience with CRF kitties - but plenty with mouth-problem kitties!!!