How old is your cat? Is it indoor only or does it also go outside? If it's very young it could have parasites that are causing this. Coccidia and giardia sp? can cause this. Rice and canned pumpkin can be used to help bind a cats stools but if the cat is very sick it should see a vet. Plain yogurt can also be given to help increase good bacteria.

What kind of food are feeding your cat? Dairy products can sometimes also cause diarrhea. My cat Starr has very bad food allergies and also colitis and he had severe diarrhea for many months. I hope that your cat will feel better soon. Please update us when you can.