My period is very weird.

I need help ladies. I don't know what's going on with my body. My period is really weird. I'm 20 years old and have sex with my partner regularly. I took birth control for three months to help out with my cramps. I've had to use plan B a few times though because we have had unprotected sex and we don't want any kids right now. In August my period lasted three weeks then it stopped. Came back a week later and continued in the beginning of September. This time it lasted like 2 weeks. Once again it stopped for about a week and I just got it again today. Could it be because of plan B? I'm thinking about going to a doctor because this isn't normal.