pregnant but concerned :( help

So my first day of my last period was November 10. I took a pregnancy test Dec 10 and came out Positive but fainted. So I went to get my first ultrasound the 4th of January and according to my calendar I was suppose to be 8 weeks but the doctor said I only measured 6 weeks. We didn't find a heartbeat either :/ she wants to see me the 18th and time seems like it's dragging I'm scared that maybe, my baby stopped growing :( has anyone been through this?