Hi!
With ds2 I was 5w 5d (knew this was 100% correct as knew my ovulation date) and they only saw a gestational sac measuring 5w 1d. I was devastated and really thought it was over. When I went back 10 days later all was well!
With dd I went at 6 weeks and saw a 2mm baby with a hb!
So a few days can make all the difference, please try not to worry yourself silly if you don't see anything as it's very normal, I wish I had been reassured this xx