My daughter and I both suffer from it. It's harder for my daughter to control it since she is younger.
I ask "strangers" because maybe I can get some good advice before going to the doctor's. I hate to say but not all doctor's know best.

Exercise, Exercise, Exercise.
Exercise will help the body both mentally and Physically. Simply running for 20 mins a day will help release endorphins which will make you feel better. Below is an article that supports this position.
I think it also has added benefits. As one exercises more, one naturally gets in touch with ones body. The body will tell you what it needs for nutrition. If you just listen to your body you will then also start eating better which will also improve your out looks. When one is working out hard it is hard to have negative thoughts. This will also help break the cycle of negativity.
Now I suggested running because one doesn't need much to start up. Make sure you have good shoes! This will prevent injuries. Now if running isn't your cup of tea then find another activity that will elevate your heart rate. The object is to have your heart rate elevated for a solid 15 mins a day for at least 5-6 times a week.
Learn to take your heart rate. Simply press your finger to your neck and count. Count for 15 seconds then times by 4. This will give you your heart rates per minute. Most people resting pulse will fall in the range of 65-80 BPM.
So to determine if you are working out to hard or not hard enough here is a simple way to find out. If after working out in the hard part of the workout you take your pulse. After 2 mins if your pulse is still over 100 BPM then you are working out too hard. If After one minute you pulse is UNDER 100 BPM and close to your resting pulse then you haven't worked out hard enough.
If you do have health issue do see a doctor to obtain their advice on any exercise regime
Good Luck!

http://mentalhealth.about.com/od/depression/a/howexercise.htm

Oh I hate my anxiety. I told the doc I didn't want pills because of the addiction factor, he agreed. I told him I drink a couple beers a day and it takes it away. He said as long as I can control it and not turn in an alcoholic, it should be fine.