Wow, when I read this, I just wanted to give you a big hug! I experienced something similiar myself when I was 17. I was diagnosed with OCD when I was 17. For months, I had obsessive images in my head of getting possessed and of killing my sister. I love my sister, I would never, ever do something like that to her. I didn't really tell anyone, was constantly terrified because of the images in my head, was convinced I was a psychopath, lost all interest in school, developed insomnia, was constantly on the verge of tears, constantly terrified, and was like a zombie because of lack of sleep. Ultimately I tried to kill myself because of it all.

I'm telling you this because I want you to know that things WILL get better. Those thoughts do NOT define you. They're horrible, scary wretched things, but they can go away, they will go away, you just have to get the help you need. Talk to a doctor, a psychologist, a psychiatrist. They can help you. Talk to other people as well, don't isolate yourself with all of this. Those thoughts are no reflection of you whatsoever. Please, please don't kill yourself. Believe me, things can and will get better. Take care, I really really hope things get better for you.