What Causes Random Little Twitches In The Body?

I keep getting random little twitches in my body, I dont know what they are and what is twitching whether its a muscle or vain, I get them in my thigs forearms and even my back. Sometimes their far more violent, they dont hurt but just last longer, its like having something vibrate under my skin briefly. Apparently a magnesium deficiency can cause twitching and spasms, or lack of sleep, but I sleep fairly well. I also get cramps really easily from sports, apparently that can also be because of magenesium deificincies. I hope you can tell me what this twitching is, as of now it causes no harm to me, but I just want to make sure its not an early symptom of anything. Oh and I am a 15 year old male in decent health.