Why do I move my shoulders uP and down?!

It could be a tic of yours. Some people with obsessive compulsive disorder have it. Is it similar to how Harry Potter acted in Order of the Phoenix? The constant twitching of the shoulders and the odd moving of the head... That's what people with obsessive compulsive disorder will do, in some cases. I have OCD myself, but I don't do the shoulders thing. Monk (from the TV show) had obsessive compulsive disorder too, and he did the twitching of the head and shoulders sometimes. Mostly the shoulders, though.

Another thing you might have: restless leg syndrome

I have it, but again, I don't twitch my shoulders, so... I would go to the doctor if you're really worried about this. If not, try to restrain yourself. That's how I stop my tics. The restless leg syndrome not so much, but I've lived with it all my life, so it's pretty 'normal' for me. It sucks when trying to get to sleep, though. :(

Sorry if I haven't helped you, but I'm speaking from experience. Good luck!

I'm seventeen...

Try to control it,

this is common with geeks, dont worry, we accept you for who you are.