I sweat at school for NO REASON AT ALL! What should I do?

I sweat at school FOR NO REASON! Sometimes I even sweat when I'm cold! And if I lift my arms, tu could see big wet circles under my arms! I read on the internet that if tu put baby powder under your arms, tu wont sweat as much but it didn't make a difference! Am I the only girl that this happens to? Can someone give me consejos on how to STOP SWEATING? thanks :)