I feel as if the past has traumatized me. Everything reminds me of it & I always have flashbacks. I hate myself for what happened & I hate other people involved. If this is all true & I HATE what happened in the past why can't I stop talking about it or thinking about it? When I don't have a flashback, I force myself to think about it some other way. Why do I do this when it was so painful?

I'm sorry you're having such troubles, most people do struggle with that, in one way or another, at some point in their lives. Everyone has woes, everybody hurts.
In the mean time, while you're waiting for that counselling appointment, or maybe there is a reason why you can't go, start doing some internet research about how you feel. Search things like "how do I overcome _______" (fill in the blank with words like: hate, bitterness, pettiness, trauma, anger, etc.). And read, read, read.
Also... Do you have a good imagination? If so, when you're thinking about the past, imagine the person you are now coming to the rescue of the person you were in the past. Now I know that might sounds a little hokey, but sometimes it helps.
Here's a couple of websites that might help you foster positivity in your heart. The more you focus on the positive, the less room in your heart there will be for all the hate and anger.
<a href="http://zenhabits.net/start/" rel="nofollow">http://zenhabits.net/start/</a>
<a href="http://happiness-project.com/" rel="nofollow">http://happiness-project.com/</a>