How come when im trying to sleep i can't keep my arms are legs from moving when i don't want them too?

You may have....: ....Something called "restless leg syndrome." this is a very annoying problem that interferes with sleep and causes sufferers to be chronically sleep deprived. Just as you are drifting off, a body part jerks, waking you up and interfering with sleep. A sleep study, which your doctor can order, will confirm the diagnosis, after which an appropriate treatment can be prescribed.

Myoclonus: Myoclonus is a brief, involuntary twitching of a muscle or a group of muscles. It describes a medical sign and, generally, is not a diagnosis of a disease. Brief twitches are perfectly normal and usually occur with the onset of sleep.