6 weeks 3 days

I am currently about 6 weeks and a few days , I will be 7 weeks on Saturday. I’ve had some on an off cramping on my right side and was sent to the er on March 13 where they were able to confirm pregnancy by labs but were not able to see anything on the ultrasound. I did follow up labs twice that’s showed levels more than doubling. I went back for an ultrasound follow up on March 19 which was just shy of 6 week mark . I was able to see the gestational sac and the yolk sac which at that point still tiny. They recommended a follow up ultrasound, they were happy with the ultrasound and my levels increasing but how they telling me we should have seen more on my ultrasound... and that the baby may not be growing or it may just be too early. Has anyone gad any experience with this?? We’re you too early getting ultrasounds. When did you actually see the fetal pole/ baby and when did you hear a heartbeat....

Sincerely a worried first time mom