I had an anger problem also, and while I certainly don't want to discourage you from getting professional help, I also want to let you know that you can start to turn it around yourself. I went through the same thing a year ago with my daughter, who is 8. She was throwing tantrums when she didn't get what she wanted (screaming, rolling around on the floor, the whole bit). It got to the point where I didn't even want to be around her. She seemed to do things just to push my buttons. I felt like the worst mother in the world because I was so angry all of the time and she was so out of control.
What turned it around for me was when I realized she was mimicing MY angry behavior (as you have realized as well) and needed more loving attention from me. Whenever I talked to her, it was because I wanted her to do something and then I would get angry when she didn't do it fast enough. So most of the exchanges we had were angry ones (instigated by me) and she started mimicing MY bad attitude! (duh! you wouldn't believe how long it took for me to figure that one out!)
Once I realized this, I began working on my patience. At first, I wouldn't remember to be patient until AFTER I had yelled at her. Then, gradually, I "remembered" earlier and earlier so that I was able to take a breath & remember to model the behavior I wanted HER to exhibit. This whole process only took about a week (luckily, I had plenty of opportunities to practice. ha!)
I also started making a point of giving her a LONG hug and telling her I loved her whenever the thought crossed my mind to do it (several times a day). I made sure that when I saw her for the first time in the morning and when she came home from school, I was REALLY excited to see her again. At first, I faked it a bit, I must admit (it's hard to work up excitement when you think you're in for an evening of battling it out, and even with the smiling "I love you's" I had to 'act' a bit at first). But after only a week, there was a major change in her behavior (and my attitude). I really started to FEEL the love I was dishing out to her. I've continued with this and I can't remember the last time she had a fit about something, and I just don't get as angry anymore.
I wish you both the best. You really CAN turn this around-- I know. But it really truly has to start with YOU and changing not only how you react to her bad behavior, but how you interact with her all the time. Thinking about how I want my daughter to act really helps me stay calm when things are going badly because I know now that I have to show her how to behave (not just tell her). I would love to hear from you in a week or so to see how things are going for you. I know this is a frustrating process, but you can do it!