Severe mood swings. What should i do?

I've had issues with stress and anxiety in the past which has left me feeling low for months at a time, severe low energy, disinterested in socializing and just extremely low. But I improved very quickly from that and threw myself into multiple tasks. It was as though I suddenly had a lot of energy. This was about 2 years ago. I've had several highs and lows like that over the next years. Recently they have been extremely severe. My moods switch very suddenly. I remember being very excited and going to meet my friends and then all of a sudden I felt completely drained and wanted to leave. It left me embarrassed and confused. And then within a week I felt a huge burst of energy. I didn't feel like sleeping and stayed awake for two days without sleeping for than two hours. Then again after a week my mood crashed and I was left feeling scared what would happen next. Its affecting my life as a student and young professional. I haven't been to a doctor yet. What should I do? Please help me.