What Causes Irregularities In Menstruation?

I am 36 years old, healthy, with two children. This last period was irregular in that I had brown discharge for 9 days prior to my period and then 2 days after. My period ended 3 days ago and I am now having lower back pain and bloating. Should I see a doctor or wait to see if it passes in a few days? I am worried about what could be causing this as I have never had bloating and back pain after a period. Thank you.