My muscles shake often, I want to know why?

I'm not exactly the healthiest on my eating habits, but I'm young and I'm not overweight at all, but my muscles are often hard to relax in full, and unless I am able to relax them fully or tense them to some degree, it appears I've got more shakes than an In 'n Out Burger on a Saturday. I really hate it cause it's just annoying and I often can't even hold my hand up and point at something without moving around in random jitters, as opposed to even the normal slow sway of a hand. In addition, it seems like if I go outside on a normal day, good weather and all, that I still get a cold shiver like symptom. If there's some way I can start to minimalize the shaking or even figure out what's causing it, I would really appreciate it!