my "8wk" appt...but the nurse didn't see anything.

Leila
So I just had my 8 wk appt, we were very excited to have our ultrasound!
However we did do our ultra sound and the nurse said she didn't see anything. She said I was measuring at 5wks and that Yes I am Pregnant. which I know she knows what she's doing. But made me confused as to myself. I'm very regular with periods. I even have a tracker app on my phone just so I can run to the store before hand. So we will be doing another ultrasound next wk to see if baby is forming. This is my second child so I'm just really confused and idk?
Has this happened with anyone? What does this mean? What can it mean?