I am never not angry. i could kill people if i wanted?

i have always been a violent person, everyone is scared of me, even my friends because i just punch them all the time. now at school i have to clench my fists because every little thing pisses me of and i want to stab everyone untill the whole world dies. today my mum gave me a blueberry muffin and i cried and punched a wall. i am a girl and even guys are scared of me. i just hate everyone and i think i would have to will to kill someone. please help.