welcome, Emma,
to the MH forums of SR!
Please read the sticky from the NY Times above; there's loads of information there.
Also, try
Bipolar II, Mood Swings without Mania; Brain Tours; Stress and Depression; Hormones and Mood; and more...
It's a great resource on the bipolar continuum. Things are not as "black and white" with bipolar disorder as was once thought.
Shalom!