I've had an ongoing skin problem with my cocker - to be fair it could be a number of issues, from food to allergies. It turns out mine has a yeast infection, his skin was quite scaley/scabby. He has had anti b's, plus an anti fungal shampoo plus anti fungal meds.
He is fed on Burns & has been on his anti fungal meds for nearly a month the itching whilst it is still there is much less and I think (crossing everything here) we are finally getting to the bottom of it
Be prepared for numerous vet visits before you get a diagnosis - because often it is hit and miss. Good luck