Plenty information at these websites.
http://www.homeovet.net/dynamic/php/downloads/dog-c8470f2c75dbe4b683205c3919ee2310/dog_diet_complete.pdf
http://www.allergydogcentral.com/
Environmental allergies are more common than food allergies, often food sensitivities are referred to as allergies.
If the symptoms have been going on for more than a year, 4 seasons without significant relief I would consider seeing a specialist and having the skin testing done (if you haven’t done so already).
Have you considered consulting with a homeopathic veterinarian?
http://www.vitalanimal.com
for a list of homeopathic vets in your area http://theavh.org/ Make sure the vet has at least 75% homeopathic cases in their practice, or you might just get the same old same old.
My dog with allergies receives immunotherapy and seems to do best with Nutrisca dry (fish) as a base food. A daily fish oil capsule. Frequent baths with Malaseb.
