Is it normal that i rub my knuckle?

Is it normal that I rub my knuckles? It's only my ring fingers. It started out as only my left ring finger, and then I started doing it on my right one too, although in trying to confine it to just my left. And this isn't regular rubbing; I pinch the skin of my knuckle between my thumb and the side of my middle finger and rub with my thumb, kinda pulling all the skin to the side. I've done it so much that I've actually eroded my knuckle skin. The skin on my ring finger knuckles is a lot thicker and more swollen then the rest, and it looks puffy and smooth. I think it started out as a nervous habit, but it's turned into something that I do all the time. If I'm not doing something with my hands, they're rubbing. Many times when I'm writing or typing, I'll take a two second break, rub a few times, then go back to what I was doing. I've also taken to rubbing the skin of my knuckles in small circles on my lips. It's so hard to stop, I do it without even noticing, and when I do catch myself, I can't find it in me to stop because it feels so good. I don't want two of my fingers to look likes freaks for the rest of my life, an I don't know what to do.