Start by listing your symptoms and how they effect your life. You did a pretty good job of that in your first post.
Cutting and drug use are very serious and signs of covering up and underlying issue.
Eating disorders, no appetite are symptoms and signs of covering up
Grades suffering effecting your life.
Relationship problems.
Feelings of abandonment can mean an underlying big abandonment issue. Not supported by your mother. Is your father in the picture?
Family history of depression. Big factor.
Sleep problems. Big symptom of depression.
Depressed mood. No motivation. big symptoms.

It is possible that it is adolecence and you will out grow it but that doesn't mean you don't need help now. My daughter had alot of problems as a teenager. We tried to get her as much help as she was willing to go to. She is 20 now and is doing great. With her family history I fear that she will have problems in the future however. These diseases can hit you at different times in your life. I first started getting major depression when I was 13.