4w5days ultrasound

Maria Julia
Had a second ultrasound today at 4 weeks and 5 days. They couldn't see a lot. Not sure about sac or anythihg. They are worried it could not be viable. I will have blood work today to check the hcg levels. Is it normal to not have a lot showing?! Only thihg they could see, was a round black (what I call is black hole). Kinda worried. Not sure what to expect. 
Update: They did an ultrasound last week and couldn't see anything but apparently the one I had today was the same measurement or even smaller than last week. Last week was only a belly ultrasound, today was vaginal.