Empty gestational sac

I had an ultrasound today and the gestational sac measured 6 weeks 1 day. However, the sac was completely empty. My OB said this is still normal for how long I’m measuring. My hcg levels tripled last week and were spot on for how far along I am. I’m a nervous wreck as I have had a previous miscarriage. My OB scheduled another ultrasound for next Wednesday. Anyone else been through this and have any positive outcomes? I’m mentally preparing myself for the worst but would love to hear some real feedback. Good and bad.

Thanks