Low HCG and slow rising

I am supposed to be 6 weeks 6 days today. When I went for an ultrasound last thursday they measured me 5 days behind and only saw a gestational sac... my HCG more than doubled in the first couple of weeks but I went for blood Monday and it is only 5,011!!! I am waiting for my doctor to call me but I am sick to my stomach. No bleeding, no cramping... I hate waiting and not knowing. Did anyone else have low and slow rising HCG?! I seriously can’t stand not knowing what is going on. 😭