Skin very itchy when hot

Hello all and thank you all for your advice.

I have a weird condition that I don't know of, so that's why I come here to do a pre-exploration.

My skin (mainly torso, back, head, very little on my legs, not at all in my face) get very very very itchy whenever I feel hot (from weather or from embarassment)

I live in Canada. In the summer, it's easily 30 degrees celsius (80 degrees Fahrenheit). That does not bother me. But if I start running, doing exercise, or I am in an embarassing situation and I feel hot, my skin gets very very very itchy. Same thing when its winter, which gets easily to -20 degrees celsius (-4 degrees Fahrenheit): If I am outside and I run, do exercice, embarassed, I get very very very itchy. Sometimes it happens also if I am outside and get inside (sudden temperature change).

The more I scratch, the more it itches. So I basically just wait for it to stop itching, which is a pain in the ***.

I should probably mention that I have dandruff and acne also. I am 20 years old male in 110$ health condition.

This condition started approx. 2-3 years ago.

But now it happens very very often and it became a problem during sex.

I am looking for advice

Thank you very much !