Well, here is a l o o o o o n g shot guess for you. My guess is that sometimes what we eat can affect our reactions to other things. In my case, wheat made my asthma worse, too much sugar somehow made my skin more susceptible to rashes.
I had a mystery rash for years. I mean, two decades. It would come and go. It was suggested I use antihistamines, topical cream . . . nothing seemed to change it. It came, it went. Was worse generally in late winter. So, for other reasons, I fasted from sugar and starch for a while. My goal was four weeks. After four and a half days, the rash in my elbows was gone. Days later, the rash on my legs was gone.
When I was found to be gluten intolerant, I gave up wheat (and barley and rye), and several months later noticed far fewer asthma attacks.
So, maybe you can try modifying your diet for a few weeks and see if that helps. It isn't a diagnosis, but if it helps your body manage better, that might be worth something.
