Call the vet and have her call you back, explain what is happening. I would try to work closely with your vet, prescription food and all.
However, since the symptoms have been going on for several months and the dog has not responded to treatment I might ask her for a referral to a specialist, either a veterinary dermatologist or an internal medicine specialist.
You can use the search engine here to look up “environmental allergies”
Example:
/forums/topic/doodle-with-allergies/#post-119649
PS: I am assuming routine labs/tests have been done and medical issues (other than allergies) have been ruled out.
