Why is my Boston Terrier's skin rashy? Food allergies?

[NUnum1]

I have a 14 month Boston and the last time we took him to the vet they were concerned about his hair loss on his hind legs and on top of his head. They said he may have allergies but they wanted to forgoe the testing for now and try Benadryl. We did that for a little while but didn't notice much of a difference. We are thinking he has some kind of food allergy. The main irritation spots are under his armpits, behind his ears, and pinkness on his abdomen.

He started on Royal Canin food and recently switched over to Nutro Natural. Not noticing any difference. We also give him the Milkbone variety pack (bacon, beef, liver, chicken) and Kong liver snaps for his treats.

Has anyone ever experienced allergies in their dogs with these foods? I would like to forgoe the testing if I could but am thinking it is the best resolution. He also has very dry skin and flakes everyday. If anyone has a good moisturizing soap/lotion to use please let me know.

Thanks!