Have you ever listened to or read Dr. Drew? He deals a lot with sexual abuse and could be really beneficial to you.
It sounds like you have had someone abuse you in the past and has made you feel this way.
I understand the cutting thing- I used to do it. I don't want to say it's "normal" or healthy, but a lot of people do this. It release serotonin and makes us feel better. That being said, you just have to fight it. When you are feeling this way, distance yourself from the things you use to hurt yourself. I have a permanent scar in a very open place that everyone can see and I regret it all the time. I hope this has not happend to you, but I urge you not to let it get to that point.
and STOP taking your brother's meds. This will do more harm than good! They were not made for you. They are made to serve your brother's needs. If you feel you need medication, talk with your doctor. They will help you.
We all have self-esteem issues- it helps to talk about them. It will eventually solve the problem. If your boyfriend truly loves you, he will help you through this.
But start out with Dr. Drew- he is awesome.
Vivre Bien