If your Dr. is telling you you are 6 weeks pregnant, that means its about 4 weeks since conception. They always count from 1st day of last menstrual period.
Fetal pole and heartbeat are typically visible anytime between 5 1/2 and 6 1/2 weeks. Sometimes a bit later, around 7 weeks. They will be able to tell you more about viability with blood draws and the next ultrasound. I know this is scary and I will keep you in my thoughts. Take care and good luck to you.
Congratulations on your pregnancy and welcome to the forum!
~Wendy
The fetal pole is normally visible sometime during the 6th week...but if you're only 4 weeks pregnant, it's definitely too early. 3 weeks pregnant would be before you even miss your period, and the embryo would just be attaching to the uterine wall around that time. Best of luck! I hope you get some good news nest week!