abnormal bleeding hormonal imbalance or more serious?

I'm 28 years old and have been having irregular periods about every 28-50 days for the past year. I am not on birth control because we are trying to get pregnant. I had my last period about a month ago and have had bleeding every ohter week since then. I am wondering if this is just a hormonal imbalance or if I could have something more serious like ovarian cancer. I have some pain on my lower left side.