My cat won't stop licking himself, I don't know why can any one please help?

This is called "over-grooming". My cat licked all the fur off her belly, but the vet said it was just stress. So we put her in a smaller place with fewer cats and she was better, but it was also recommended that we get some "Feliway", which is calming to cats. You plug it in like an air freshener. It's almost like magic!