I have a cat that is 3 years old. Probably for the last 2 years she has had diarrhea on a regular basis. Its terrible, her butt is always dirty and she is a white long-haired cat and that makes it even worse. I have another cat that is prone to UTIs so I feed them a Urinary Tract health food, I feel like this is more serious than diarrhea but sometimes I wonder if she is allergic to something in the food. I need to know what kind of food to feed cats with both problems and also they are very picky, two weeks ago I tried to switch to Natural Balance, for the first time Stella was clean and didn't have diarrhea but my other cat wouldn't eat the food. What should I do???