Stewie was on the Metronidazole for about a week, he got a quarter pill every 12 hours. It seemed to help for the first 3 days, and then the messes downstairs started up again. He weighs a healthy 11 pounds.

Thanks so much for your insight on this, I'm definitely going to research giardia and see if that matches Stewie's symptons before I call the vet today. I feel sorta weird suggesting things to her...after all, SHE'S the expert here. But, I guess I see Stewie on a daily basis and know his behavior better than she does. It's definitely strange- I have no clue where he might've picked anything up from. He stays indoors and wants nothing to do with the outside world at all (I think because he was an abandoned kitten, he was found in a soccer field). And my other cat is very healthy, has no problems whatsoever.