Plan b effects ???!

Lizbeth
Im not sure what to do ... or to think that my period came super early. But my last period I started on June 30th and ended July 4th. And today is July 16th ... and it's been a heavy flow... and the color of it looks a bit darker than usual... can someone tell me if it's normal... or is it a side effect of plan b? I took plan b on the 9-10th.