6w5d ultrasound...no baby?

I had some very minor pink spotting this morning, but just to make sure, I called my doctor. Since I was worried they told me to go ahead and come in and they will scan me. I wasn't sure of my due date before, but they said I'm measuring 6 weeks 5 days. However, all they could see was the gestational and yolk sac. She said both look very healthy and it's possible that it's just too early to see an embryo. Has anyone had anything like this before? I'm so worried!