Cat is itching and hair is thinning- dermatitis? infestation?

My cat is a Maine Coon and has extremely thick hair. Awhile back someone brought a pet over to our place and we ended up with a really bad flea infestation; our siamese was hardly toughed but our furry boy got it bad. We got it all cleared up, but he was allergic and left with a sore spot by his tail that was raw and thinning from itching and biting. It healed up, over a year ago, and now seems to have started up again. I am absolutely certain its not fleas; also we have not changed his food, and I cannot think of any other irritants. His fur isnt visibly patchy, just thinning, I think from him pulling it out constantly itching. There are tiny scabs across his backside and creeping toward his head now. Today I noticed in a spot where he had been laying, several tiny things I thought were scabs but look exactly like strawberry seeds???I tried to look under a magnifying gl but too small for detail. Maybe some kind of insect shell? Or dead insect? They are teardrop shaped and kind of brownish yellow I suppose.....Anyone? Also, please let me know if you know any good websites with this sort of information, especially with images. Thanks!!