Pink spot, then light period+bad period cramp

My bf n I had unprotected sex on the supposed day of my ovulation but he pulled out and we never did second round. A day before my period is due I've had one or two spots of pinkish blood. My period did come on the next day but it was alot lighter than usual and I had very bad stomach cramp which I never had on the first day. Today is my second day and my period is still lighter than usual, and my cramp is gone for now. When I said light I meant like 2/3 of my pad is still actually covered with red blood. Can implantation bleeding be this heavy at all? Not to mention having very bad stomach cramps and blood is red