Memory loss- What is wrong with me???

i am 16 and have no memory of before 9 years old. before i moved in with my dad i lived with my mom who had drug problems, we were also on welfare and my sister was ually abused by my moms boyfriend. both of my sisters have memories of these things but i have none at all. My stepmom thinks i surpressed the memories but it affects my life now because i cannot stand being touched. I freak out on people- even my little brother when he clings on to me but i dont know why. I also had severe depression up to fourteen and that had just recently fadded.