People gave advice before, but this recent post is too vague for anyone to be able to answer.
What shampoos? What prescription food? How long ago did you see the vet, and what did the vet recommend? Does the vet think it is allergies? If so, food allergies or some other type of allergies?
You've just reminded me that I need to go clean the ears of my latest rescue foster, who had poorly managed ear issues for 10 years and needs to have me use ear cleaner on her once a week.