Hcg levels and early ultrasounds

So l am currently 4w6d super early I know. Last night I was having some cramping more so one left side and for over an hr. I called my drs office after hrs line and they told me go to the ER. When I went I got a bunch of tests. My hog was 571 and when they did the ultrasound there was no sac identified at the time. They want me back in a few days to recheck everything. I'm concerned about ectopic pregnancy.

Has anyone else experienced this? What were your heg levels early on. When I was pregnant with my daughter I feel like they were super high at this point.

Anything you can share would be great...I'm super nervous.