Question.. RN or blighted ovum experience?

I have been cramping from the beginning of my pregnancy, which is why I had originally thought that my period was coming. At my 6w2d ultrasound, both sacs were there but fetal pole and heartbeat were not detectable. I'm either too early or experiencing a blighted ovum. I understand that the nausea and sore breasts are caused by progesterone and that HCG still rises for a while with a blighted ovum, but would I be cramping if an embryo wasn't burying itself in my uterine lining? Do you cramp as a result of hormones, or the burrowing/implantation only? I'm still cramping as I have normally with no bleeding.