Vet gave me eye drops and antihistamine...eye drops are working, but the antihistamine isn't. It's not a food allergy. No change in diet. It's a spring time allergy (she had it before). Last time, they gave her a steroid shot and it cleared up. This time they didn't, so she is still itchy. Central Texas allergies are the worst!!

Make sure his diet has plenty of animal fat...unlike humans, dogs use fat as their primary source of energy & healing, have no cholesterol issues. I had a dog that would get Huge hot spots overnight, so much so the vet allowed us a stash of antibiotics when we traveled, to minimize their spread. I tried every food additive on the market, a laborious process becauseskin takes 6 weeks minimum to show any effects....keep this in mind!
Finally, through luck, I found UNsalted butter, about a tablespoon a day added to high-fat high-protein dog food. Gleaning coat, no more ear infections, NEVER another hot spot, and she was a hunting dog & field trial champion constantly wet, muddy, outdoors, etc.

Take it you've tried exclusion diets. Dairy seems to be the one that gives a lot of dogs trouble and the whey protein found in a lot of dogfood is still dairy.

Bummer - try diphenhydramine which is plain Benadryl. My vet suggested it for my dog. She said I should give her 50 mg (2 regular tabs). You can get generic diphenhydramine. If you get Benadryl, make sure it contains only diphenhydramine as they also sell it with a decongestant. Dosage is approx 1 mg per 1 pound of body weight, 2-3 times a day. My dog weighs just over 50 pounds, hence two regular 25 mg tabs.