Was the ultrasound a vaginal one? If she did it straight on top of your belly there's no way they would've seen anything. I had a vaginal ultrasound at 5w 3d and we saw a sac only, no heartbeat. So don't be too worried, checking your blood hcg results and making sure they rise is the best way to know what's going on when it's this early.
The dr. Told me I needed to wait till I was about 8 weeks in order to see something because before that your too early you wont be able to see anything jst a little spot if your lucky I still have t wait 2more weeks im so anxious^.^
The same with me I was 3 weeks when I found out and all they saw was the sack
That happen to me with my pregnancy before my first baby . Got blood work and everything done and showed I was pregnant but when I got the ultrasound done at 8 weeks , the sac was there but no baby at all .... Hope that by time you alil further along , it shows there's a baby .
This is going to sound bad the way I put it sorry in advance. At 3 weeks baby isn't even the size of a blood clot. Most ultrasounds can't see the baby till 6 or 7 weeks. If the test came back positive then your pregnant just not far enough to detect with an ultrasound
Same exact situation I was in and now I'm half way thru my pregnancy, Dont Worry and congratulations .