Is this normal?

Amber

I’m due sep 4th I had an early ultrasound at 4 weeks and 5 days and there was a sac but no yolk sac or anything else is that normal or should I be worried ? I go back next Monday I’ll be about 7 weeks then. My friends was only 5 weeks and a day and she had a yolk sac but I didn’t so I’m super freaked out. I have a baby already whose 9 month old but I didn’t have an app till I was further along and I could see the baby well then.