Dr didn’t confirm pregnancy but kept saying possibly?

I told them I tested positive on two sticks but on both one line was faded... everyone kept saying congratulations and the urine test was positive but even then the dr said “I think you might be you are 5 weeks and something days”. She talked to me about options but said we would have to wait for an ultrasound to confirm? What are the reason... can a urine test lie? I feel like they keep getting my hopes up by saying I might now be and in the end when I’ll be pregnant.  Is there a certain week that doctors have to wait to confirm? And how early can you detect a baby through ultrasound?