6 Week Ultrasound - yolk sac & gestational sack

I went in for an emergency scan this evening and HCG beta draw. My previous HCG results were;

5 weeks 2 days - 4600

6 weeks 0 days - 9600

and this evenings 6 weeks 2 days was 20,461. the ultrasound showed a gestational sack and yolk sack but that is all. my uterus was not cooperating so she couldn't see if there was a baby and said it might be too early. has anyone else gone through this?