Questions questions

It's been roughly 2 weeks after my miscarriage and I have so many questions in mind. I'm still not understanding how one week an ultrasound showed 9 weeks and the next it showed 6 weeks. Like does the baby shrink ? Or what ?! I don't understand it, if it stopped growing at 9 weeks shouldn't it say 9 weeks with no heartbeat ?! I keep tutoring myself and looking at "Miscarriage but still pregnant" on Google bc I'm still feeling sick and all and not to mention it happened to my mom when I was supposed to have a twin.