I think I'm addicted to overdosing, how can i stop?

I started overdoing as a form of self harm but now i just cant stop. When i think about it my heart just starts racing and i feel like i have to. It feels like all this pressure is building up in my chest and it wont go away until I overdose. I cant stand to have pills anywhere around me and not take them all. I'm really scared i'm going to kill myself! I dont want to be like this and I really need help, does anyone know anything i could try or has anyone been through this? I would really appreciate your help!