6 weeks no heart beat

sandy

So I’ve had 2 miscarriages in the past. I was supposed to be 6 weeks 5 days and went in for an early ultrasound. The baby measured 6 weeks 1 day and no fetal pole or flicker seen or heard. I feel like cause I did the trigger shot I know exactly when I ovulated. But is this normal? How early can you hear the heart. And is it ok to be measuring 4 days behind.