i dont know what it is, depression maybe?

Okay, i need someone to tell me whats wrong with me, because obviously i cant work it out myself.

Im 17, and even though im very young, i dont know who i am. my personality changes alot, and most of the time im pretending to the person somebody else wants me to be. i dont know how i got my head into this mess, but i can never think straight. I never know what my next step is, and even though i try to have fun and enjoy my life, it only lasts for a few hours.
Maybe its been cause by the constant conflict between me and my father. Or maybe from a past experience where i got pushed around and hit alot by an ex boyfriend. Ive never been an open person, so i never mentioned that to anyone, except a friend of mine witnessed it.
I did well with my GCSE's but i stil dont know what i want to do, im going nowhere and the longer i spend dwelling on the past, the worse my life seems. I dropped out of college because i couldnt afford it, and i felt alone. Now i work in mcdonalds and thats never where i intended to be. When i was in school i always had ambitions and goals but ive dropped them all.
I always feel alone, and in need of company. I have had other boyfriends since me and the specific one above ended our relationship, but in every one of them, i am a whole different person at the beginning to what i am a few weeks/ months in. Also, when a relationship comes to an end, i have to have a new guy around because i cant be single. I dont understand why.
On many occasions i have cried myself to sleep at night, or i have sat outside in the pouring rain just staring into space. i dont know why im like this. When i was younger i had my head so straightened out, i knew what i wanted to do and who is was. I was happy. There was one time when i considered suicide, i thought about it for hours on end but in the end i couldnt do it. So i guess im not too bad, but i still feel like i need help. I dont want to open up to anyone, i trust nobody, not even myself. I cant tell my mother or anyone how i feel, and i really cant explain myself, its hard enough to write it all here. I feel like im closing off from everyone i ever cared about and i cant stop myself.

Is anyone else the same?