If you feel like you're two different people, and injuring yourself you need to see a psychiatrist. The "two people" thing could be bipolar disorder, borderline personality disorder, or multiple personality disorder, but I'm not a doctor. Especially since you're harming yourself, you need to see a specialist ASAP. Ask a trusted adult for help in finding a psychiatrist who can help you.
For the self-injury part, contact: 800-366-8288
It's a free hotline that can help you.
Good luck.
I Agree With Dara, You Need TO See A Docter To MAke Sure That You Stay In Best Health :)