What's wrong with me?

For the past few years, I've felt off. Since I was maybe 12/13ish. I'm now 17. Some days I feel amazing. Actually so high up. It's wonderful. I'm energetic and motivated. I'll feel like that for weeks, even months at a time. Then randomly one day it'll drop. I'll take a complete turn. I won't want to eat or see my friends and family. I won't have motivation. I don't even get out of bed. I don't shower and my hair matts to my head. Then after a while, I'm back to normal. Sometimes I don't feel either of the two. I'm just me. I don't understand it, and I don't know what to do. Am I broken?