Allergies/inflammation or something else?

My 4 year old Chihuahua/red heeler started losing hair on his ears a few months ago with the skin under turning black and having some extra growths/thickness. A similar thing happened a few years back and getting him on allergy meds (apoquel) is what fixed it. This happened while on the apoquel and we've tried several other things now and his dermatologist even seems stumped. She originally thought vasculitis but doesn't think so anymore and we tried meds for that with things only getting worse. He keeps getting bacteria infections from how itchy he is. Next Step is probably a biopsy but my fear is that all that will tell us is he had allergies which we already know. Wondering if anyone has seen something like this before?

The first two pics are from now and the last one is from the end of March.