I'm wondering if I'm suffering from minor depression or bipolar?

For the past few months my life has been crazy. Actually, I've been crazy, not the things in my life. I'll be in school and I'll have random crying spells and I would have random depression moments where I just shut down and stop eating and snap at anyone trying to talk to me so that I will be left alone. Sometimes (not often though) I'll have suicidal thoughts. I'll think I have depression and feel very secluded and such. But then I'll get super angry all of a sudden and I get over myself and stop being sad and just being super peppy but also really pissy and easily agitated. This has only been happening for the past 5 or 6 months though, so I don't know if it's a mental disorder or if I'm just.