4 day long implantation?

Having really awful "period cramping" a week after my period. I'm not ovulating yet so it's not that. My period was only 4 days long and it took all day to fill up a pad for all four of those days. Could this have actually been implantation bleeding? I'm also very nauseous and (tmi) having lots and lots of white, creamy CM.

Any of you ladies had this before? What are your thoughts?