How to get over the negative experiences I had in the past?

Hello doctor,

I am an 18 year old female. I have been feeling low. I feel sad, irritated and angry most of the times. It has been going on and off this way for the past five years. There are certain eating issues too. I do not feel like eating. I do not get hungry. I just eat one meal a day. And sometimes when I do feel like eating, I do not because I get scared I will put on weight. All this started five years back. I was in class nine when my section got changed. So, my grades started dropping, and my relationships with friends, teachers, and my parents became worse. It was like everybody hated me. My mom thought I was a burden. I got very very jittery at that time. Once, I was at my table studying, when my dad came from behind and suddenly pulled me out of the chair and slapped me. I got so scared I wet my pants. After that, sometimes I became very jumpy. I would freak out even when I heard the sound of a door opening. Although I am not so scared now, I still feel low. I recently met a counselor. She advised me to talk to a psychiatrist and she mentioned the possibility of depression or PTSD. Is it possible that I could be undergoing either of these? Which of these two do I have? And, what should I do now?