Does Bleeding With Black Clots Occur Due To Implantation?

Hi, I was supposed to be due for my period on July 18th (8 days from now). I started having brown light bleeding yesterday. Today it is black and clotted and a little heavier. I should have ovulated on July 1st. At first I thought this might be implantation bleeding but it seems to heavy, yet it is nothing like my regular menses. Help?