This is terrible! Your mom is abusing you. For reasons I can’t begin to understand only on the basis of a letter, she seems to be reliving her own adolescence through you. It strikes me that this is the emotional equivalent of Munchausen by proxy, a mental illness where a mother makes her child sick in order to get the attention she craves from doctors and hospitals. Your mother is manipulating your social life so she can get some thrill out of the drama of it all.
I’d like to think you could start with your dad. If he’s not aware of what’s going on, by all means tell him and ask for his protection and support. If your dad isn’t the kind of guy who can stand up for you, then you really do need to involve another adult. Talk to your school counselor or nurse or a trusted teacher or your doctor. Ask them to help you get in touch with the child protective services in your area. The abuse needs to stop. At your age, you need to be figuring out relationships and developing your own friendships. Your mother is robbing you of the experiences with others that will help you make good choices as you grow into adulthood.
You absolutely shouldn’t hurt yourself out of anger and frustration. Same goes for dropping so much weight. You are already being hurt too much by your mother. You don’t want to be hurting you too.
If you need support while you work things out, call the Boys and Girls Town Hotline (800-448-3000). There are counselors there 24/7 who can talk with you and help you make good decisions.
I wish you well.