Severe mood swings, self harm tendency.

My moods switch very suddenly. I feel irritable at times and it goes on for days. Sometimes I'll feel very light and happy and then suddenly I'll feel extremely low, even suicidal. I've tried to self harm to distract myself from the pain. It gets unbearable, then it suddenly gets better again. It hurts my social skills. 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 am a good student but I've always had issues with losing interest on things easily. I haven't been to a doctor yet as i feel i'm making things up. I want to have a healthy life. Please help me.