Empty sac and HGC levels?

I went into the doctor for my first ultrasound and the nurse found the sac but it was empty with no yolk sac or fetal pole, according to my LMP I should be around 7 weeks but the sac was measuring 5. My periods are pretty regular and they did blood work and I got the results and my HGC was 9,172. I’m am going back in today for more bloodwork to see if it has doubled since Monday or not, I’m just curious (and worried to death) if anyone else has experienced anything similar and what the outcome was?