Oh OP, I'm so sorry for your loss. What a terrible thing to happen
I also had a D&C after a m/c at 18 weeks, and there was some "retained product" still left inside my uterus (ie: a small bit of placenta was left accidentally). This caused me huge amounts of cramping and bleeding. I went back to the maternity ward and had an ultrasound which confirmed there was still a bit in there. I was sent home and able to pass the tissue naturally (without medication to make my body do it). If my body hadn't cleared it, I would have had to have medication to force it, or otherwise another D&C. I got my period 35 days after the m/c and D&C. I usually have a 28 day cycle.
Perhaps your cramping is just AF or O cramping, perhaps it's something more. Do you have a temperature? Are you bleeding? Go to your Dr or the hospital if you need to check it out.
As for sex, our m/c has significantly effected our sex life and I've been chronically depressed since it happened almost 3 months ago. But I am getting better, and feel I'm "turning the corner" now with the grieving process. I guess it just takes everyone a different amount of time to get over this kind of trauma.
*hugs* to you, hon xoxox