I did a search and found this regarding what an ultrasound would show at 5 weeks on *****************.org
"Week 5 - Gestational Age (Fetal age 3 weeks)
Development
The gestational sac is often the first thing that most transvaginal ultrasounds can detect at about 5 weeks. This is seen before a recognizable embryo can be seen. Within this week, at about week 5 ½ to the beginning of the 6th week, a yolk sac can be seen inside the gestational sac. The yolk sac will be the earliest source of nutrients for the developing fetus."
So...a gestational sac is all you would expect to see at this stage.
If your doctor is concerned, he or she will usually schedule another ultrasound in a week or two to measure the growth between the scans. He/she will also probably order serial blood hCG tests, two blood draws taken 2-4 days apart to measure your hCG levels. The levels should double about every 48 hours.
how do you know you are 5W5D did the Dr. measure during an US and tell you that is how many days you are, or is that based on your last menstrul period? At 5W5D your Dr. would at least be able to find a sac, and they might or may not see a heartbeat. Some girls you dont get a heartbeat until 8 weeks. Did the Dr. tell you to be worried?