[QuickSilver]

How regularly do you find fleas on him? I see you live in San Diego, do you walk him on the beach? I ask because one flea bite will literally make Thor itch for three weeks. And while I am not completely sure, I think fleas can still bite your dog even if he is on a flea treatment - they just can't live on him. So if you are finding a flea every two to three weeks, he won't get any relief. If it's frequent, I would suggest finding another area to walk him.

My understanding is that the first step to identifying an allergy is an elimination diet, and then if that doesn't help, testing for other allergens.

I'd also recommend keeping a log. It will help you a lot in identifying the root cause; otherwise, it's probably all going to start blending together in your head. Good luck!

I've also heard that fleas don't like the smell of lavender, so maybe look into putting lavender oil on him. That's one of those folk remedies, I don't have personal experience with it.