When I first took my dog to the vets with it, he gave her steroids, they cleared it up to begin with, but within a month the rash and itching was back. A further course of steroids had no affect whatsoever. So IMO a waste of money.
There's so many allergies that can cause skin conditions in dogs and I would strongly advise an appointment with a Veterinary Dermatologist, as diagnosing and treating something like this is beyond the scope of an ordinary vet if the treatment they have prescribed so far has failed.