Help!

🎀Michelle🎀 • I`m a 25 year old mommy of a perfect son and a beautiful daughter! I am pregnant with baby number 3 due Feb 8!
Had An ultrasound this am according to my LMP I should be 5 weeks! My sac is measuring at 6w2d! All we saw was sac and yolk sac no heartbeat?  What's going on? I'm anxious now!