6weeks, 6days pregnant and no fetal heartbeat, is that normal/common?

Yes. Unfortunately miscarriages are common. It is estimated that one in every 2-3 pregnancies ends in miscarriage. As our ultrasound has gotten better, we are starting to see more fetal demises on ultrasound. I look at it as something along the process of development from our heads down to our toes probably didn't develop quite right and the baby could only grow so much with that malformation.
Very common. In very early pregnancy heartbeat may not be detectable, even with ultrasound. Wait a week and check again.
Yes. At this early gestation the viability of the pregnancy may not be able to be determined particularly with transabdominal ultrasound. If the lmp is off you could actually be earlier than you think--too early to see a heartbeat. The key is the fetal size. If the fetal length is >5 mm, a heartbeat should be identifiable. If <5mm, a repeat sonogram should be done before diagnosing a failed pregnancy.