You can use the search engine here to look up environmental allergies.
Until you get the environmental allergies under control, changing the food will make little to no difference.
For the best results make an appointment with a veterinary dermatologist (asap).
If the symptoms have been going on for 1 year 4 seasons without a significant response to treatment by your regular veterinarian, it is time to consult a specialist.
You could ask your veterinarian about an elimination diet/prescription food, if you have not done so already. However, food allergies are rare and food sensitivities fluctuate.
Don’t be fooled by saliva and hair food sensitivity mail-in tests (scams).
If you are receptive to science based veterinary medicine, you may find this site helpful
http://skeptvet.com/Blog/?s=allergies
The veterinary dermatologist will accurately diagnose your dog, then you can evaluate your treatment options. Best of luck.
This is not veterinary advice; consult your veterinarian.
