How can someone overcome depression and suicidal thoughts?

Hello doctor,

I am a 20-year-old female. I have suffered from depression since I was in junior high school. My parents are strict, and they put such high expectations on me that it became a heavy burden on my shoulder. Since then, I have always thought about committing suicide; I think I am not good enough for anyone and that I am better off being left alone. People around me keep telling me to be positive, but I do not know why it is difficult. They say I am being dramatic, and I choose to suffer like this, that everything is on my mind. Maybe they are right that I am an ungrateful human being. That is why I distance myself from everyone and dislike myself. I often run out of breath just thinking about what a terrible human being I am. I sleep way too much and eat way too much. Hilariously, I feel constantly exhausted, and I keep losing weight. I often think about running onto any bus that comes through on my way to work or home. I never take medication. I cut myself sometimes to put myself at ease. I work out so that I can focus on something. Is there anything I can do to heal myself?

Thank you.