Q: Nothing showing on first U/S

laymel

I found out I was pregnant on Monday and had a confirmation appt with my doctor on Tuesday. He advised that I was about 6 weeks based on my LMP (which I'm not 100% sure on the exact date - I'm pretty sure it was sometime within the last week of Sept so I could possibly even be 5 weeks depending on what day). He scheduled me an u/s for the next day. While there, the tech kept making weird faces the whole time and asking me over and over again when my LMP was. After what felt like an eternity, the tech advised that she is showing a gestational sac, but nothing else so she figures I am only 4 weeks. She has scheduled me to go back on the 21st to confirm a date.

 I've been driving myself crazy since it doesn't make sense to me that I would be 4 weeks if my LMP was the end of Sept...

Anyone had something similar like this happen?