Afraid i might miscarry

My last period was July 31st - Aug. 2nd. After taking multiple negative pregnancy tests, I got a positive blood test September 9th.

I went to get a ultrasound today thinking I’m about 7 weeks and it was only a empty sac 😞. I’ve been doing research to find that it’s a thing called “blighted ovum”. The doctor said she think I’m just very early but that can’t be true when my last period was July 31st.

Just really worried, this is my first time being pregnant and i have no idea how any of this work 🥺.