Sac but no baby?

According to my last period I’m supposed to be 6 weeks today. I went to get an ultrasound and had the sac but no baby was seen. My test are coming out darker and darker though. I’ve had an ectopic pregnancy before but that didn’t go last 5 weeks and I had heavy heavy bleeding and no symptoms. This time I’ve had a few symptoms that have gotten worse in the last 3 days. Dr said everything is fine and I just need to go back for another ultrasound in two weeks but I’m so scared of it being another ectopic pregnancy. Has this every happened to anyone? The ultrasound wasn’t vaginal