This happened to me with my daughter and she is a healthy seven year old now! It was very stressful when it occured. You may even be earlier than five weeks. When it happened with me the doc did what Sheri recomended! Many well wishes to you!
My u/s yesterday also showed gestational sack and nothing else. I was 5 weeks 4 days. I can totally relate to your stress. I hope your next u/s shows a strong h/b!
Thats nothing to be worried about. They start to grow rapidly now, and a day or two can make a huge difference. I am sure all is fine,
Good luck.
At 5 weeks, they didn't even see a sac with me, so I wouldn't worry quite yet. It takes until 6 weeks or so to see a heartbeat and fetal pole usually, which is what happened in my case! I was worried too but all is well! I am now 17 weeks and baby is kicking me in the bladder repeatedly! :P
If you are really concerned, have your doc do a series of Beta HCG tests 48 hours apart and if the number is going up (roughly double every 48 hours), everything is fine!
Sheri