Ovulation bleeding? And why?

So I have only bled once while ovulating, which was last year. I now have bled while ovulating the past 2 months. My periods are regular and last 4 days every time. I went to my OB to try to find some answers, but I did take a plan B pill for the first time, so she though that might be the case for bleeding off my period and also try to get me on birth control, which I do not want. I am just wanting to know if this is normal and or why is this happening?