why am I sweating so much ?

I never used to sweat excessively or anything but one day in school (I've just turned 16) during drama after the play I got mad sweat literally dripping from my hair which I've never had before and ever sense it even the smallest tasks or walking fast or anything will cause me to sweat excessively especially from my scalp under my hair. I never sweated in my sleep but a few days ago it started and it's just been the same like this morning when i woke up my top was wet with the sweat and the whole way up my head. It wasn't too warm in my room and I was only wearing a top so I couldn't've been over heating. It's freaking me out a bit is this normal??