Can't stop messing with my head.

AHHH. I'm 21 years old. I constantly pick at my scalp, and I don't know why. It's not because I feel like I have 'imperfections' on my scalp. I just do it to do it I guess. But anyway, I started doing it around this time last year. I went on a hike and I was wearing a bandanna. I was sweating A LOT and after the hike, I felt little bumps on my head, that turned into scabs over the next few days. Ever since then, I've been picking the scabs off. I haven't created new scabs or anything.. I just pick the same ones. I picked at one spot so bad, it created a bald spot about the size of a dime. And it's right where my hair parts!!! I find myself picking when I'm doing things like watching TV. My hands just go up there and I run my fingers over my head and pick them off. I don't pile them up, save them or eat them. I just throw them in the garbage next to my bed. I also feel around lightly for dry flakes of skin and peel those off. Again, I just throw those flakes away. I also squeeze the black spots I have on my nose, and the pus or whatever comes out. This causes my nose to dry out, and it makes skin flakes show up. And, you guessed it...I peel those off too. I just don't get why I started doing this. It hurts. I don't enjoy it..I just DO it. I also blink my eyes harder and longer than normal people do. I feel like everyone notices..I don't know if they do, but it still drives me insane to think they do. How can I stop doing this? I do have depression and anxiety. I am a heroin addict. When I started picking, it was about a month after I got out of rehab. So maybe it's a nervous tick I have? I don't take any medications either. What's WRONG with me?! ):