Do you have a compulsion?

Like, do you an activity or thing you have to do? For example, if you are just sitting there, not doing anything, does your body just randomly start going through the motions of that activity? No matter how hard you try to stop, you just can't? That's a compulsion. It's a mental thing. 
According to Wikipedia...

"Compulsive behavior is defined as performing an act persistently and repetitively without it necessarily leading to an actual reward or pleasure"

I have one of those, you know. It's a nasty one, I'm just going to warn you. 

I compulsively pick at my skin, specifically sores. You can't really tell from just looking at me normally, but I have several open places on my back and thighs, combined with many small scars. It's absolutely disgusting. But I just can't keep from doing it. 

Like, when my mom starts griping at me to stop picking at them, I'll be like "Okay! Starting now I will stop!" and then in a fit of boredom a couple days later I'll suddenly look up and realize my face or my ear is bleeding. There's no control and it's killing me. 

And if I consciously make an effort not to do it, I start feeling all twitchy and anxious. I just start scratching at the healthy skin on my arms (a nervous tick of mine) because I just feel so weird.