Hi, Do you have regular cycles? What is the date of positive pregnancy test? What type of ultrasound you had? Abdominal or internal? Do you have bleeding? Yes it is possible to identify gestational sac at 5 weeks and embryo at 6 weeks by internal ultrasound. By abdominal ultrasound you usually see gestational sac at 6 weeks pregnancy. There is always a possibility of delayed ovulation and delayed conception. So don t panic. Take the medications prescribed by your doctor and repeat ultrasound after one week. At this time you should see embryo. I wish you good luck.