Hi Carol, just some questions, how long since the flea issue was resolved? If recent, you need to give your cat some time before seeing fur growing back. Second, did the Vet check for other issues such as fungus or allergies? If that is discarded your cat may have developed a behavioral issue that comes with anxiety with is over grooming. The typical area where they lose hair is in the flank section which is the muscular lower part of the body, between the lower rib and the knee or thigh areas. This is called psychogenic alopecia and you need to enrich your cat’s environment, behaviour modification through training and if the case is bad, medication. You may need to check with a Vet to discard these issues. But first wait about a month to see if your cat’s hair has grown. Hope that helps!