Yolk sac but not fetal pole

Desi

So from my last peirod I should be close to 7 weeks but when I went in to get the ultrasound all they saw was a Sac and the yolk but no fetal pole. My doctor called me and said she thinks we are around 5 to 6 weeks instead but I have to go in for another scan in a week. Im freaking out though. I cant stop thinking somethings wrong. Has this happened to anyone?