Boston Terrier with a neverending rash?

I have a Boston thats less than a year old. He has had a rash of some sort for about 6 months now. He has red spots and he scratches them and makes bloody gross spots. This rash is not isolated to one area. Its all over him. I took him to the vet about 5 times now with no luck. He was given prednisone and an antibiotic. It helped for about 5 days then the rash cam e back. This has happened at least 3 times. The vet says he thinks its allergies, but has no other treatment ideas. He gave me Revolution for fleas, so I don't think its a flea allergy. I've switched foods, laundry detergent and dog shampoo. Nothing has worked. Any ideas? I'm going to try another vet, and I hope I find something soon. He's not easy to cuddle with anymore and its making me crazy. Thanks in advance.