Arm picking HELP

So I have those chicken bumps on my arms, legs, thighs, and butt. I constantly pick at my arms, specifically my right one (probably because I’m left handed) and I pop sebum out of the bumps. I believe it’s called Keratosis Pilaris. HOW do I stop? Why do I do it? I also chew my cheeks constantly and bite through the flesh until well past the point of bleeding. WHY. And what can I do to stop?