Dates doctor predicted vs what the ultrasound said

Hey guys, I’m 7 weeks pregnant exactly, yesterday (6 weeks 5 days) I got my first ultrasound, the lady suggested that I’m only 5 weeks 4 days pregnant, however I missed my first period almost 3 weeks ago and have had bad morning sickness for the last week which I was told often doesn’t start until 6 weeks onward. Not only that, but we could see the baby’s heartbeat clearly and she said it doesn’t usually form until 6 weeks?? I’m so confused as to my actual weeks now.. Bloodtests were taken by my doctor at 4 weeks 1 day, almost 3 weeks ago now and my HCG levels suggested I was 4 weeks pregnant at that stage. So I’m confused as to how this has happened? She did say that she’s unable to get an entirely accurate date/measurement but suggested I get a vaginal ultrasound to increase the accuracy but I figured I’d trust what she said seeing as I saw my baby’s healthy heartbeat anyways. Has anyone else had similar? Based on what was said do you think she’s accurate or the doctor and my assumptions are more accurate?

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