Question on diarrhea

[Lernermichelle]

So Lucy still has diarrhea, going on a week now. It started a few days before her surgery, I think from my switching her diets too quickly-- she had been on S/D only for about 6 weeks, and I stupidly switched her to S/O over only two days when it was clear her bladder stone was not struvite and had gotten bigger rather than smaller on the S/D.  She had been on Baytril for a month at that point too, because without it she kept getting UTI's due to the bladder stone. Since 2 days after surgery she has been off the baytril, but I have had to switch her food again (this time i am doing it slowly) due to finding out her stone was ammonia urate (neither struvite nor oxylate). She has been on Metronidazole for 4 days.  I am concerned, because I have never seen diarrhea in a cat take longer than 2 days to resolve on Metronidazole, and the vet seemed surprised as well. I have been giving her slippery elm, and today started giving her a feline kaolin diarrhea over-the-counter med.  I gave her acidophilus for a few days after stopping the Baytril.   Any suggestions? Also, have any of you ever seen diarrhea persist for over a week, with no other symptoms, from something like antibiotics or dietary change, but then resolve in a little more time?   Thanks, Michelle