Omg, yes. Cotton tshirts are the worst. Just go to target or Ross or Kohls and they will have a good selection to choose from.

You need wicking material. It pulls the sweat away from your skin. You can get these anywhere and spend as little (Target, Old Navy) or as much as you'd like (Under Armour, Lululemon)

I've been wearing just cotton t-shirts to the gym and getting very over heated. The best thing would be to be able to control the a/c, but since I can't do that, is there a different fabric that would help me feel cooler?