Hi everyone! My ultrasound dating differs a lot from the obstetric (LM…

Hi everyone! My ultrasound dating differs a lot from the obstetric (LMP) dating. According to my periods I'm at nine weeks; a week ago I had an ultrasound and they dated me at 3–4 weeks, the gestational sac was 12 mm, the embryo wasn't visualized, only the yolk sac. Two weeks ago I also had an ultrasound: the gestational sac was 2.7 mm. Has anyone had something similar? I'm very worried and don't understand what my actual gestational age is.