I constantly pick at my head?

For a long time now, I've had the habit of scratching/picking at my head. It's not because it itches, or anything, I just do it, it's almost like a stress-reliever for me. I do it espeically when I feel anxious/stressed and I just love how it feels. It comforts me almost. Although, sometimes, I can scratch off scabs/moles that are on my head, even though I know that's probably bad, but I can't stop. Even if I try not to do it, I will end up doing it anyway, sometimes unconciously before I realize what I'm doing.

I thought that maybe I had Trichotillomania, but it seems to only apply to people who pull out their hair and I don't do that. So, don't know what's wrong with me, and if anyone else even does this.