Okay, I reread your post. I sometimes get carried away when discussing allergies :/
Anyway, you could try a grain free limited ingredient food, my dogs do well on Nutrisca salmon and chickpea.
However, for my allergy dog, the food is only a small part of the treatment, but in conjunction with the other treatment modalities, it works (as a base).
If you noticed positive results with the prescription food, I would go back to it, at least till the dog is stable.
Again, I still think a veterinary dermatologist would be your best bet if the symptoms continue.
