Scratching my thumb

Hello. I've had this problem for 3 years. I pick the outer sides of my thumbs with my nails but mostly with sharp objects even with a fork. My skin has changed its color and is very thuck even though it's easily cut by the sharp objects that I use to scratch it. I don't feel an itch but I just have the urge to do it. I do it all the time. I kinda feel relaxed while I scratch until i accidentally cut my skin. It's become numb and I can feel almost nothing when I touch it with my fingers. But when I start scratching it, well, it feels very good. I'm sorry if I gave too much information but I just wanted to share my story. How can I stop myself? Can my skin recover or it's permanently damaged? Please, answer if you have the same problem!!! Thanks.