Will Falconer, DVM Moderator
Best place to point you John, is a post called Itchy Skin Wins Big: Vets Scratch Their Heads. Likely the missing piece of the puzzle for you.
That, and the services of a vet homeopath to undo the damage done. See my Resources page for the AVH list and get someone from there to help get to cure.
Your dog shows a very strong vital force, popping out pustules after all the suppressive drug therapy. Strong vf = good prognosis for homeopathy to cure.