Sweating too much?

Okay so lately I’ve noticed that walking to class this winter at about 28°F that when I get there and take off my coat and sweatshirt that I’ve sweated a lot. Like enough to be able to see a dark sweat mark on my back. It happens too when I’m wearing just my sweatshirt and a long sleeve walking in 40° weather. I normally have my backpack on with a notebook and laptop in it while I walk to class (at most 15 minutes). Am I sweating too much or am I super out of shape? (I probably weigh around 130 lbs ish)