Ultrasound 2weeks behind


I took a test when I was 3 days late, it was positive. According to my LMP I am 8 weeks. Well today I had a second ultrasound due to spotting for the last 3-4weeks.

The last ultrasound the could not see a fetal pole. Today however, they said I measured 5weeks 6 days. I am so confused as to how that is even possible. I am very worried something is going on.