How can i sweat less?

Im 12 years old, and i know its normal to sweat (pubertyyy) but i have this one shirt i looove to wear but it's tight and grey and when i wear it i get big stains under my arms. I wear deoderant with antipersperant, and it helps a little, but not all the way. It doesnt smell, only stains. Is there anything simple i can do, preferably at night or right before school, that will make me sweat less? and im not worried about the smell so please no crap about bacteria i already know that.