Implantation

Is it possible to have early implantation? I've read that it's usually between 6-12 days but also read stories of it happening earlier. I'm 4 DPO and I've had mild cramping in my lower abdomen and pelvic area, and also a tiny bit of spotting of which I've never had before in my life. We BD 5 out of the 6 days(including three days before, on, and the day after ovulation day). Any input would be great.