I think my pit bull is allergic to something.....?

My blue pit bull is 6months old and 50lbs. He seems to be mentally and physically healthy, he eats at least 2 out of 3 of his meals a day but some times he seems to be a little to mellow at times. I think he might be allergic to something, I just don't know what it is. He gets these little bumps all down his spine and back. You can only really see them when you look at his backside at an angle in the light. I can see the bumps protruding through his fur, some of them are fairly big. I tried flea spray and bathes, but they are still there. His eyes are also red a lot of the time. I feed him Purina Pro Plan for pups and I bathe him every week. I'm scheduled to see a vet next Tuesday, but I want to get some feedback from any pet owner who might of experienced this with their loved ones. Thanks!