@anon212494: It has been my experience that mood swings are often triggered by blood sugar imbalances. Eat small meals throughout the day to keep it in check. Be sure to eat whole grains and lean protein, as these digest slowly, keeping the sugar stable.
If your diet is less than perfect, be sure to take a multivitamin that is heavy on the B-vitamins. These help to regulate mood as well. I really notice a difference in my mood when I pay attention to my diet.
You could try some herbal supplements as well, like valerian, kava kava or SAMe.