stop picking my skin

A little bit of late-night Wikipedia trawling has ended here, with my realisation that I might actually have a problem. When I was younger I used to pull out my eyelashes and eyebrows (though I must admit I still pull out eyelashes from time to time), but I seem to have replaced that with picking at my skin.
Three things I thought were just bad habits of mine, it turns out, might actually all be part of the same condition. There are scabs on my scalp that haven’t healed for about five years, because I cannot stop picking at them; any time the merest blemish appears on my face, be it a pimple or just a tiny lump, I pick at it until a terrible red crater is all that’s left; and, perhaps worst of all, I tear my fingers apart until the tips are raw and bleeding.
I always told myself I was “neatening up” the dry skin, but I recently realised that it gets so much worse when I’m stressed, angry, or sad. My fingers are pretty good at the moment – only one is slightly shredded – but uni exams are coming up and I can feel myself starting to pick at the others. Now that I’ve realised what I’m doing isn’t just a bad habit, I’m determined to stop it.