Why do I think this, please help?

I'm 19, female. I grew up in a house for half of my life that was full of domestic violence and such until my father was kicked out. It really took a toll on me mentally until the age of about 17, since my father didn't care about anyone else but himself, me and my mom struggled all my life. It was hard seeing my mom go through so much pain and knowing I was powerless to stop it, and it really sparked a rage in me. I always had my fathers temper but I was full of plain rage. I started to calm down and realized I needed to accept it and move on, because it was holding me back. I'm still working on it, it doesn't happen overnight. But anyway, I am a bit overweight. And I have been made fun of for it, but I know I am prettier then most girls so when someone does say something to me, it really doesn't bother me. However for the past two months I can't go outside because I have a phobia of people seeing me. My mom thinks I'm lazy but I hate looking at people and feeling like I know what they're thinking. I always have my guard up. I'm always ready to fight as well. When I'm out with friends its almost like I want someone to make fun of me so I can hurt them really bad. I always hope it happens. Why am I thinking like this? I'm a really nice person.