possible miscarriage?

This past period was very strange for me. I had cramping at 6-10 DPO, with cramping so painful it woke me up in the middle of the night at 10DPO. I had my period after my normal luteal phase of 15 days but the first day was very heavy which is not normal for me. I tested negative at 10, 12, and 14 DPO but I wonder if I did conceive since the flow was heavy that first day. Has this happened to anyone?