Shaking uncontrollably?

Lately, I've been noticing that when I am excited about something or if I am anticipating something, my arm starts shaking uncontrollably. Sometimes my arms just stay by my arms and shake, other times it stretches out and then starts to shake. Yesterday, my friend also noticed that when I was holding a camera to take a picture of her, there was a tremor in my arm. I don't notice the tremor in my arm but my friend says it's quite noticeable. I'm a 14 year old guy, please help! :) Is this an issue that could affect my health? Could these tremors be symptoms of something bad?