Okay help

Okay so went in for an early scan at 6 weeks 2 days and no heartbeat could be seen and I was measuring 5 weeks 5 days. I have a repeat ultrasound on Friday and I’ll be 7 weeks 6 days. I have barely had pregnancy symptoms except sore breasts and some light cramps. Should I be worried ? My doctor said that I should except to start bleeding but it’s been a week and nothing . I just need to know if this is normal or this has happened to anyone else ?

Nervous and thank you