I used to before a shrink I went to told me I have bipolar disorder. It's not a terrible or embarrassing thing, as many seem to think. Could just be your hormones, but if you have them ALL the time, it can't hurt to ask your doc :)
Everyone has mood swings, whether they admit it or not. Females are more prone right before or during their periods. If you're having wide mood swings on a regular basis, you need to see a doctor to be tested for Bipolar disease - which can be treated with medication.