6 weeks, high hcg, no heartbeat

Went to get my first ultrasound at 6 weeks because I have a history of 3 previous molar pregnancies and I'm at very high risk for another. My hcg was at 19,600.

They saw the gestational sac and yolk and what she thought might be baby which measured 5 weeks 6 days. But there was no heartbeat. They don't seem concerned and said it's probably too early; but other than bloating I have no symptoms and I did with my other 2 kids. And hcg of almost 20,000 is really high and should definitely see a heartbeat at that point.

I'm freaking out as this is my last chance for another baby