Severely scratching ears.

I've taken my dog to 3 vets so far for "allergy" symptoms. His episodes start with head shaking, then scratching at the ears (the ears are clean), even going as far as "grinding his ears on concrete", panting, then he'll lay down and go through what can be best described as a seizure as he frantically rubs his nose with his front paws. I have no doubt whatsoever that anxiety takes over. During the episodes his body odor turns horrible and I'd swear he just turns insane. I do all I can to calm him down (petting, scratch his belly, etc.) but the only thing that seems to help is diphenhydramine.I bathe him weekly with hypoallergenic shampoo. These "episodes" happen at any time of the day or night. I've done everything the vets have suggested with the exception of allergy testing (Cheapest I found was $700)- change the food, no treats, muzzle him on walks so he don't eat grass. Is it possible having him neutered would help? Is there anything else I can do for him? I would be extremely grateful (as would Tattoo) if you can give me the answer that the 3 other vets missed.