Why do I feel this way?

There was a point when I thought that I was doing better. But now it just seems that things are slipping right back to the way that they used to be.  There are good days and there are bad days, but recently the bad days have just been getting worse.  I have reached the point where I can no longer just put on a happy face and go outside.  Just this afternoon I went for a very long walk, but you see the  problem is I can walk away from facebook, and my cell phone and whatever is going on in other people's lives but there is no place for me to run that will get me out of my own head.  I want it to stop already but no matter what I do or what happen it just keeps coming back, but worse and worse. It is like taking one step forward and then another five steps back.

I have been reading up on depression and have found that in most cases there is something that caused the onset, but I have not yet been able to figure out what triggered it in my life. Perhaps its from my sparatic childhood with inconsistent friends, and lack of social life. Maybe it is my inability to figure out where I fit in, whatever it is, it is hurting me in places I don't want it to.  I fear that it is hurting the one relationship that I don't want to hurt, but since he is the closest and really the only person that I talk to as a really close friend he is the one that I lash out on. I want to stop but don't know what to do anymore. I want this all to just go away and let me live my life with out any more depression.