Poor guy - it's awful to watch them suffer like that

. So, with the Orijen and Wellness - are those the regular that you tried or have you tried the 6-Fish or Ocean? Because a fish kibble might be worth trying here if you haven't already.
Just a thought: have you ever had a skin-scraping done on him, just to be sure nothing is going on there? It might be worth the $28 (approx) to rule out a few things, just in case - you could check for mites, mange, yeast. I mean, I doubt it's those things - but it might be worth knowing for sure.
I checked pollen.com for you - and it looks like FL right now is low/med - so it could be seasonal, but again tough to say - but it's something for you to keep an eye on, along with his symptoms. So, maybe check the site once a week along w/ keeping an eye on his symptoms to see if you can correlate anything there.
Lastly, I'll mention feeding raw. I feed raw (NV) and really like it for my guys. Some folks on here have switched to raw after seeing itchy problems and have seen great results - so it's something I'll just toss out there. It doesn't always solve everything - but for some it has.
Anyway, I do hope he finds some relief - poor little guy. Fish can do wonders sometimes too.