U/S - only saw sac?

So I’ve had some brown spotting when I wipe for a couple days so I went into my OB this morning. When they first looked all looked normal. She said it was on the outside of the cervix and most likely my cervix was just reacting to all the changes. Based on my last period I was expecting to be around 7w3d so they took me for an US. When they did the US they only saw a sac but no fetal pole. I’m going back next week but didn’t know if anyone’s had this happen and what the results were?