How does picking start?

Hi, my name is Ali and I've been picking for about 7 years. I started just like normal, picking at scabs, bug bites, imperfections on my face, and the little bumps on the sides of my arms. I don't do much of that anymore, I was lucky enough to never really get acne often but when I do I picked at it and picked and now there are plenty of scars but nothing noticeable really (I guess that's because I use makeup to cover them up) Anyway.. What I do now is I pick quite often at my scalp, and my back. Sometimes I'll be sitting in a car, or bored at work, at a movie theater, or watching TV at home and I'll just subconsciously raise my arm and run my fingers through my hair, using my fingertips to find any little flakes of dandruff or old scars or anything. I have designated spots where I frequently pick too. On my scalp, I have (right now) about 5 different small areas where large scabs have grown from my picking and I continue to pick until it bleeds and then just pick at that when it scabs over. I won't even notice I'm doing it until I realize my fingernails have blood underneath them.. Usually about once a week, once my scalp gets way to sore to even touch, I'll move on to my back and feel for any scabs or bumps or anything to pick at. My back is the worst, the amount of scars along my spine is disgusting looking, I can't even look at it in a mirror without wanting to cry. There's always new big red bumps from where I pick, and I can't where any pretty dresses or shirts, I'm constantly covered up. I actually decided to go swimming once at the hot springs here, because there were no red bumps for once, only just the dark scars and little scabs in very few places.. I figured it wouldn't be too bad. I actually had people staring at me and my friend wondering why my back looked like I had thousands of freckles where the rest of my skin was without any at all. So back to wearing normal clothes.. Anyway, I don't even know how picking like this started.. I'm not generally depressed or anything, but I guess I do have a bit of an anxiety problem and I turn to picking whenever I get anxious. It just calms me down, and it doesn't always hurt so I guess I don't think anything of it. I tried to stop for a week once, and I went an entire week without picking! My scabs on my head cleared up, but the scars on my back remained, and my scalp still had several little pimple-like bumps that never went away, so being upset, I resorted to picking again. Now it's just a hundred times worse, and it's killing me. I'll sit in front of my mirror and pick anything on my face to get rid of any bumps or imperfections, and I'll do that for hours. It's taking control of my life and I can't seem to stop it, and I don't know how or where to start...