I also get these unwanted thoughts in my head. I'm fighting to stay positive. When a bad thought comes I tell it to "Shut up" or know that it's not true. When I think about harming myself I think about people's reactions and my future and that helps stop me. Keeping myself constantly busy distracts me from bad thoughts. I don't know if I'm helpful, but I'm starting to become more positive. I wish you the best.