I was convinced that sex caused my first miscarriage, seeing as it happened the morning after we had sex. But my OB assured me that there was nothing we could have done. I am very sorry for your loss, I know how hard it is.
I am so sorry to hear about your loss. I agree with Kellmom, though. Chances are there's nothing you did or didn't do to cause the miscarriage. Most miscarriages are caused by chormosomal problems, where the embryo starts growing, but as it gets to the stage where it needs that certain chromosome to continue developing, the pregnancy ends.
As for the spotting, some pregnant women do get that after intercourse, since the cervix is extra sensitive during pregnancy and there's more blood circulating "down there."
Take care of yourself, OK? I've had two miscarriages myself, so I know how heartbreaking it can be.
It can be hard to say, sex does not normally cause a problem if it is a healthy pregnancy, but I am surprised the doctor did not put you on pelvic rest. You probably should of stopped having sex if it was causing you to bleed, but it being the only reason you lost the baby is hard to say really. Healthy pregnancies normally have no issues with it.
I am sorry for you loss!!