Anybody good with calculations before I have surgery for MC

This is my first pregnancy. My husband and I had intercourse on sept 18 to be exact. I hadn’t had sex before then because I was healing from a surgery on my knee. I also remember getting the happy face on my ovulation stick later that night after intercourse. I THINK my last period was September 4 or 6 but I seriously can’t recall. Sept 8th at the latest 

I took a pregnancy test roughly three weeks ago and got a positive with a faint on 9/28 as a matter of a fact I took 30 over the last 2 weeks because I couldn’t believe my eyes. A few days later I started spotting with light pink blood only when I wipe. Me as a first time mom I panic and got an appointment. At that time I was 6 weeks and my blood work came back good with 3900 HCG. Doctor said she had no worries and everything looked fine no ultrasound was done.

Approximately Two weeks( 7days 4 weeks based on my calculations) later I don’t feel the same so I go and get an ultrasound from the people who do the 3D ultrasound today and she tells me she see a gestational sack and yolk sack but no baby. IM CRUSHED. She measured my yolk sac and said I was maybe 5 weeks and 5 days. 

My next appointment was today and all my excitement is gone. I’m suppose to be exactly 8 weeks. I got a transvaginal and she said there was no baby but she did see a gestational sac and yolk sac. My husband thinks I miscalculated.

of course the doctor said I had a missed miscarriage and tells me my options to speed up the process with surgery, Pills or naturally wait.

ugh.... what do I do. I’m so hurt. We are hurt.