I only just skimmed through the posts, so I might be a replaying record – but if you’re not able to track a food suspect, it might be environmental allergies. I heard you mention mosquitoes – that’s very possible, also some dogs are sensitive to grass, pollen, etc.
Maybe try adding a little spoonful of raw organic LOCAL honey to his food daily and see if that eventually helps. I’ve heard of honey working miracles on itchy allergy dogs. If you want a “quick fix”, then you could try Benadryl (or the equivalent for dogs, I’m assuming you can find allergy tabs)
