How do I stop myself sweating so much?

I'm a fifteen year old girl and I have a problem with sweat. No matter how much deodorant I wear, it's still there. Even if it's cold, I sweat. It's becomming a problem because it dominates what I wear. I can't wear certain colours and usually have to wear a jacket to cover up the sweat patches. Like I said, deodorant does nothing. I am fifteen so do not want to try any extreme measures. Help?