What Causes Constant Light Spotting?

I am 35 yrs old. I have always had regular menstrual cycles...2 days heavy bleeding followed by 2 - 3 days light bleeding. I started my normal period 13 days ago....two days heavy bleeding, followed by 3 days light bleeding. I thought I had stopped bleeding on the 5th day, but every day now since (so for the past 8 days, I have had some light bleeding). Is there possibly something wrong?