Why Won't Kitty Stop Grooming?

I'm having a slight dilemma with one of my beloved kitties. For one reason or another, he will not stop grooming himself. He licks and cleans nonstop. Normally this wouldn't be an issue, but he is starting to lose fur in some places on his body where he is constantly licking - on his belly and hind legs. One other cat owner that I spoke with is also dealing with this problem. We are both worried that we will have bald kitties if we don't figure out a solution.

The vet did give me a few ideas, so we are trying to narrow them down.

Here they are:

Fleas

Cats will obsessively clean themselves if they have fleas. They feel the little creatures crawling on their bodies and try to pick them out of their fur. I've checked out my kitty, and not a single flea has been spotted. Of course, that does not mean they don't exist. I live in a warm climate, so fleas are always hopping about. I applied some prescription Revolution to my cat, in hopes of killing the creepy crawlers if they do exist. So far, no results.

Allergies

Just like humans, cats and other animals can suffer from allergies. Instead of presenting with the normal runny nose and watery eyes, they may have extremely itchy skin. When scratching doesn't calm the itch, your cat may instinctively lick the area over and over again. I really think that this may be my cat's issue. The vet would prescribe Prednisone for this, but we want to wait to see if the flea medication works first. Steroids have a long list of side effects, and they should only be taken when necessary. Besides, allergies can be seasonal, so hopefully the itching will resolve on its own.

Anxiety

The most difficult to diagnose is anxiety. If kitty is not feeling content for one reason or another, he may be licking as a way to calm himself down. When I got this cat, he was abandoned by his owners. They left him without food and water for who knows how long. He didn't have a good temperament, but I worked with him everyday to help calm his fears. Anxiety could very well be the reason for his grooming. If he has memories of abandonment, he may always fear the worst.

I'm not going to give up until I find a solution to this issue. He's not hurting himself, but he does look really silly with his bare tummy and hind legs. Please stop grooming, kitty!