Only gestational sac..

Kayla • Pregnant with my rainbow baby! Baby#1🖤🤞🙌🤱🤰🌈 September, 2019!✨🌟🍁🌎

I just went to the doctor today to get an ultrasound, and she said that I was measuring at 4 weeks and 6 days. We saw the gestational sac, but no yolk sac or anything. Is this normal so early in the pregnancy to only see a gestational sac? Just a little worried. Thank you for you opinions!!