Oh Randi! I'm so sorry I missed this thread until today
I do hope that Fister is doing/feeling better. I had a male cat sometime ago that had some problems with this, however not as bad. The Science Diet Prescription food was all that he could eat, and NOTHING else (not even treats )

I also heard somewhere that a little apple-cidar vinegar in the water helps (I would check on that before you try anything at this time, since he is so sick) I know the vinegar is quite good for us people for so many things including urinary tract.

Let us know how it goes, and I will be thinking of you and sweet Fister!