I don't know what to do anymore?

In October 2010 I got my first horse. An 8 year old oldenburg/TB mare. When we went and looked at her everything was great! When she came home it was a totally different story. She is now extremely speedy, pulls/holds the bit, doesn't stop swishing her tail, throws her head up in the air, falls through her left shoulder and everytime you get her moving with her not going through it she drops it right away, always has her ears back, and never stops getting faster if you don't have a strong contact.I have tried EVERYTHING from medical to technique. Nothing has helped. Whenever we try something new I always think it's gonna be better. I almost always end up in tears when riding her and it's gotten to the point were coming to ride her is a chore. I wanted to move up and start the 3-3 6 jr. equitation in shows and that's why we got her but I doubt she will ever be a good equitation horse. I doubt we will be able to go to any shows because she is just not going well. I have no idea what to do anymore. What do you think?