Did an ultrasound at 4 weeks and the results came back that they could not see a gestational sac... has anyone had this before?

Keep in mind this ultrasound was to check a cyst, not pregnancy, but that did come back in the findings.

I have to do Serial HCG next week, but my pregnancy blood test came back as 45 and that was in/around 3.5 weeks. Also just did a urine pregnancy test after getting the results of ultrasound and it’s a blazing positive. 5 days deep in my missed period.

Freaking out a little after my last MC!