Implanon does all sorts of weird things to people's periods. Personally when I had it in, I would generall only get very light periods after long breaks between (six months in between). One of my friends would get very extremely heavy ones with lots of clotting and very regularly (evey 2 or 3 weeks). So it may not have been miscarrying, just rather how the lining in your uterus is forming and coming away with the changes brought about by your implanon.