If you can, give up the self mutilation. If you feel compelled to hurt yourself, talk to your parents or a trusted adult as soon as you can. If for some reason you don't think you can talk to your parents, talk to a school counselor.
If you have suffered physical and mental abuse from your parents or another family member, then talk to your school counselor immediately. Examples of physical abuse would include beatings, inappropriate touching, regular slaps across the face, and other attempts to hurt you physically. Examples of mental abuse would include repeatedly being told negative things about yourself, being called insulting names, and being threatened.
Only a medical professional such as a psychologist or a psychiatrist can determine whether your symptoms or behavior would indicate depression, bipolar disorder, or some other condition.
Being a teenager is not easy. Don't be too hard on yourself, and try not to take out your frustration on yourself or on others. I think it's good that you posted here asking for advice or help, but I recommend strongly that you contact a local counselor, psychiatrist, or psychologist to discuss this face to face. You may find that difficult to do, but I think you'll find the effort will be worth it.
Once you've contacted a counselor or medical professional, be open and honest about your behavior and your feelings. It is their job to help you, and they will do what can be done to help.