Thank you for opening up and being so honest with us, it is a very personal issue that you have explained to us, but it certainly puts things in a very different light.
I am extremely disturbed to hear you have such low self esteem that you would want to end your young life,I can only imagine how frightened your parents are after this happening, as a parent I would be beside myself with worry, I know when I am very worried I sometimes come over as being angry too, so please try to see this from their perspective.
They simply love you to bits sweetie, and are so scared they may loose you, they probably don't know how to be with you, they seem to be making some mistakes, but they are obviously worried and concerned about you, even if they reacted wrongly by hitting you, and i cannot condone that part of their behaviour at all whether it be once in a while or not.
Have you as a family try some counselling, because it sure sounds as though you all need some help here.
please never ever consider that option again, everybody's life is worthwhile, you are on this earth for a purpose sweetie, please make the best of what you have, life has so much to offer, you just have to reach out and grab it.:)