Think it measures from conception. Based on that you are likely in your 4th week leading to 5th week because an estimated date is based on the first day of your last period 😊
Book yourself into your gp for later this week to get your bloods taken, they will check everything from blood type, immunization etc. ask for a referral for an ob if going private. And if u want a dating scan ask for that ask well, ask them if there are any bulk bill places in ur area.
Congrats again, so very exciting!!!