EARLY ULTRASOUND.... no yolk sac?

Rachel • Ig: rachel_marilyn follow me and let's keep in touch
So went in today.... based on the first day of my last period ( oct. 10th ) I'm five weeks. Realistically I'm like 3 weeks. ULTRASOUND showed a uteran sac but no yolk sac. And no baby. My Dr. Said to come back next week, to see if maybe it's just too early and if something shows up next week? Does anyone have any thing similar or experience?  Kind of freaking out.