U/S has a plus or minus factor of about a week. If he is telling you the sac is measuring 6 w, 3 d, he is referring to how it should look if you were 6w, 3d from the first day of lmp. So your dates are off by about a week and a half right now. That is close enough that they could chalk it up to your dates being wrong. Is that a possibility? Don't worry about when you had actual intercourse. I know it's confusing, but the date of intercourse is not usually the same as the date of conception.
I think we talked about this before, but just in case...
Sperm can live in a fertile environment for 5 days or so. So the actual egg can be fertilized long after you had intercourse. It then takes a few days to implant, sometimes up to 10 days. This is why they measure from first day of lmp.
I'll be honest with you. Even if you were 6w 3d, at this point they should see more then just a sac. I've been down this road a few times now, and I know that is just really hard to hear, but I have to be honest. This does sound like it could possibly be a loss. If this were me, I would request another u/s in a bout a week. At that point there should be a heartbeat for sure.
I'm sorry your going through this. I know it's scary and so hard. Unfortunately there is nothing to do right now except wait and see which is the worst emotionally. Hang in there honey, and I'm so sorry this is so stressful.
The only other thing i know is on2/12 my preg test was positive. So im assuming i conceived from the 4 th. Idk if that means i ovulated late or not? And i guess this week would be 8. Idk u think i am too far along and not to see the yolk! Im just scared. Sorry.
So...how far along should you be...about 8w?? you honestly could have ovulated late...i went in for my first sono at 6w and there was no baby...went back a week later and there it was...my dates were right cuz at the 7w repeat sono i measured 6w6d...im now 22w. Dont lose hope yet!! :)