Emotional swings are always big problem, particularly because no one understands you. Consistent depression is probably somewhat easy to handle but not the cycles of elation and gloom.
You need to bring balance inside you. In my opinion you may try few things almost simultaneously:
1. Eat regular meals and strictly avoid fast food, caffeine, and alcohol.
2. Sleep sufficiently. If there is problem sleeping play some brainwave entrainment audio and sleep (if need guidance, read my hub on brainwave entrainment)
3. Read my two hubs on mental chatter. You will learn to handle your negative mental chatter.
4. Train yourself to think that feelings are not permanent. When feeling low consciously think that it will not last forever and pump up yourself with some deep breathing.
5. Finally, think about the big picture meaning of life. Bad and painful things happen to GOOD people.
Emotional balance and strength are the keywords for you.