Why do I sweat so much?

I'm 12 years old and I have been sweating so much under my arms recently. I'm too embarrassed to take off my jumper at school because my arms will usually be wet. Even when I am just sat on my laptop or watching TV or reading a book, I will be sweating. I asked my Dad about it and he said it's normal for my age. I understand that, but nobody else (and I mean nobody) sweats like me. I asked my Dad about this and he said, perhaps they aren't developing as fast as me, but every other boy at school is tall, muscular and have deep voices. I recently saw a Lynx Dry advertisement on the television but I do not know whether it would be worth buying. I have Right Guard at the moment but it's no better than the shop brand! What should I do to control my sweating? It's getting really annoying!