Why do I itch so much?

So, last year I asked a question similar to this, something along the lines of “what’s wrong with me!” I’ll pose the question again, because this hasn’t gone away, it’s actually come back worse. I know it’s stupid to ask medical questions on the internet, but I’m not exactly looking for solutions so much as suggestions. Or maybe if someone has the exact same condition, to tell me what they’ve figured out.
I itch, at lot. At school when I get flustered I itch. When I laugh I itch. When I’m nervous I itch. If I’ve been out running and I come inside I itch.
I find that it only happens when I get warm – so the tiny classes at school which are pumped full of warm air are a nightmare.
Usually I’ll begin to feel a tingling here and there, my shoulders, hands, knees. Then the tingling becomes the need to itch, I feel hot, flustered, and usually end up removing my sweater (if I have one on, which I usually do). There is visible symptom on my skin, aside from turning a little red.
In order to relieve the…discomfort I’ll run outside if I can, usually striping down into my boxers (if I’m at home). At school I’ll usually stuff it for a bit, then when I can’t concentrate any longer I ask to go to the bathroom and then run outside to cool down.

Last time I asked this question I was suggested an antihistamine , as it was most likely an allergic reaction. I’ve tried this and it’s not done anything (no worries Shilolo, it was a great assessment). Last winter it was bad (when I asked the question) when it died down and I forgot about it all summer.
Now that it’s winter again, it’s coming back.