Hcg levels

Hey everyone so my last period was November 24th-29th I took a pregnancy test on December 20th at night and there was a very very faint second line so then the next morning I took another one and it was a little darker but you could def see the second line. So far my hcg levels were moving up as it should have well by my period idk if im 7 weeks today or what I may have my calculations mixed up. Yesterday I went for a vaginal ultrasound and there should’ve been a heartbeat but I guess there wasn’t and inside of the sac they said hasn’t grown in the last 10 days...they’re thinking maybe this will be a miscarriage but I’m praying for the best in this. The OBGYN I go to might have my period mixed up they believe it was Oct 24-29th. But it was Nov 24th idk if anyone has went through something similar or know anyone that has gone through something like this. I have to go back Monday morning for another hcg level test.