Worried and Confused

Went for my second ultrasound and doctor said based on gestational sac looks like I am 7 weeks pregnant. However based on my calculation, as I ovulated later, I am supposed to be 6 + 4 weeks. Anyways it was saddening to find out that I had an empty gestational sac with no fetal pole or heartbeat. Doctor has asked me to come back in a week time to scan again. Any advice or experiences from any mummies here.