6 weeks and no heartbeat

The past 24 hours have been a freaking roller coaster. I went in on Monday due to cramping (which could be normal but they wanted to do an ultrasound to see where the baby was and make sure not ectopic). The doctor didn't see anything but the sac (measuring around 5 weeks). She check d progesterone and serial growth hormone levels- all which were fine. I had another ultrasound Friday morning and the OB couldn't see the baby so she sent me for a better ultrasound. On the better ultrasound they saw the baby and yoke sac, both measuring 5w6d. Because they couldn't see a heartbeat the doctor in the radiology department prepped me for terminating the pregnancy or miscarriage. Doesn't that seem a little too soon? I've heard some women didn't see their babies heart beating until their 8 week appts! Thoughts? Anyone Else not see the heartbeat at 6 weeks but saw it later? I feel like it's too soon to just say things aren't right when EVERYTHING is measuring perfectly (hormones and the sac/fetal pole) there just isn't a heartbeat right now!