Why can't I stop picking at myself? (especially scabs)

I self harm now and again but I can't keep myself from ripping open the scabs, keeping them from healing right. I was thinking that maybe this was just another form of self harm but I don't do it conciously. I don't have a trigger for it. I don't have to be upset. In fact I can be perfectly calm and content and I find myself doing it. Sometimes when I get up in the morning I am almost late getting ready because I get stuck in this trance like state where I have to get every little scab. Something else I frequently do is I will bite the skin around my nails so often and so much that sometimes they will just start gushing blood. I do it without even thinking about it. And it doesn't matter how much it hurts, I have to get every tiny sliver of skin. Another behavior I used to struggle with somewhat like this is I used to pull my hair out one strand of a time for periods of time. Sometimes I'd even do it in school without realizing it. I even had bald spots. (I havent done that since 4th grade though) These behaviors really do make daily living difficult because I have social anxiety and sometimes it draws attention. Any thoughts?