If you don't trust the vet, get a reference from a friend or someone you know and go to another vet. You should NOT feel like the vet just took the cash and didn't give a crap.
It could just be the food though that is giving the dooger skin allergies.
But that's a big could given that it could also be something else.
I don't know how long it's been since the dog has stopped eating but if it's more than 1 day, then this requires another vet visit. If this were my dog, he would be seeing a new vet asap just to be safe.