A high percentage of skin allergies are flea related. If you have good flea control then you should have the dog allergy tested. My friend just had her cocker tested and his is mostly diet related. Changing food has already helped him.
I have had to give Claritin to a couple my old dogs when we know we're going to hunt in fields full of ragweed. They'd get watery eyes, sneeze and one even wheezed. The Claritin & Benedryl helped.
Prednisone isa wonderful drug but not something you or your pet would want to be on long term.
Check with the national breed club, some breeds are prone to allergies of certain types especially in Southern climates.
The thyroid can also cause skin conditions in dogs. The omega 3 fatty acids are good for coat and skin.