extremely heavy period if pregnant?

I had a post a few days ago, asking if there was a possibility that I could be pregnant, and I had a super super heavy period in September, but none in October. Which may make everyone think that I had a missed period, but I have EXTREMELY irregular periods, and this isn't the first time this has happened. (Not me worrying if I'm pregnant, but the no period for a whole month.) So, if I am pregnant, how did I have an extremely heavy period? We haven't done anything since my last period, the last time we had sex was before my period in September. Please explain? I'm worried, and excited at the same time... I don't want to be pregnant right now, I'm so young, but I've always wanted to be a mom... I just need some clarification, everyone is telling me to test, but if I had a period, and we haven't done anything sexual since, how could I be pregnant?