What Causes Irregular Periods?

I am a 43 yo woman diagnosed with perimenopause. My last period was July 28, 2010. I was told after that long of a time I would probably not be getting any more periods ( my Mom's change of life was around age 44). I just started bleeding the past 2 days, definitely heavier then spotting but not very heavy like my past periods. Concerned if this could be a symptom of something serious. Please advise. Slight lower back pain and cramping and less appetite but manageable with advil. Thank you- Jennifer