No sac on ultrasound yet

I’ve had two ultrasounds, one last Wednesday and one today and they still can’t see a sac at all in my uterus. If I am right on my calculations I would be 4 weeks and 6 days, MAYBE a day or two earlier if I ovulated late. Is it normal not to see a sac by now :( I had had a beta done today and I’ll have he results tomorrow. Very nervous :(( any experiences are welcome.