Implantation?

Kathleen • 29 year old pregnant with #2
So as of today I am 13 DPO. Have been testing every morning for the last three days and all BFN. Yesterday morning I had small amounts of light brown spotting when wiping, and have been experiencing mild cramping. AF still has not shown, and my period cramps are debilitating where I typically have to be in bed with a heating pad and always near a restroom. 
I am hoping that this may be implantation, and I was wondering what others' experiences with implantation bleeding and early pregnancy cramping were?