Chronic rash

Hello, everyone. My problem is not as severe as many of the ones I am reading about here. My heart goes out to you! I do want to ask for advice and insight, though.
I've always had random itchy rashes that come and go; they're usually written off as allergy or hives. Since late middle age (I'm in my late 60s now), I've tended to get a persistent rash on my upper body (upper back, shoulders, sometimes arms) in late winter and early spring, when my skin has been covered by clothing for a long time. One year, I was wearing a down vest all the time and the rash got much worse, so it may have something to do with heat. Sometimes the rash is a loose collection of bumps, a little like mosquito bites. Sometimes it's just red, itchy swelling that later leaks fluid. It takes a long time to die down in the summer. Then in recent years, my skin has tended to flare up, itch, and break out in bumps just from irritation. I can't wear T-shirts with loose sleeves any more, because the tickling seems to set off this reaction. Bra straps are irritating, too; I take off the bra at home. The back of my hand also flares up, but the rash looks different there – it's more like flat white spots. The really funny thing is that I get the rash far more on my left shoulder and arm than on my right. Could it be neurological? It waxes and wanes, but is pretty much chronic at this point.
I made an appointment with a dermatologist a couple of years ago, but the office assigned me to his PA, and she was useless. She thought it had to do with dry skin caused by winter air. I think that's nonsense, because the skin on my back and shoulder is not dry, and because it was never exposed to the air.
I don't use a lot of cosmetics. I can't track the rashes to any changes in soap or anything. I like to use unscented products, or those with essential oil for fragrance.
Any thoughts? Thank you so much!