6 weeks 2 days too early for US?

I had an appointment for US when I am 6 weeks and 2 days but it has been rescheduled because my hcg is low still (based on one drawing - still waiting for second). Is this normal to not be able to see anything when you’re that (not) far along?

Also, my progresteron is low. I started bleeding a bit more since yesterday (before that I only saw a little bit of blood when wiping, sometimes). If I start taking progesteron now, could it stop the bleeding? Or am I too late? Anyone any experiences?