Hcg Quantitative 18,742

My quantitative was 18,742 at 5.5 days pregnant (based on ultrasound) today the doctor called me and said that kinda high and that I may be further along then expected (which doesn't seem possible because the ultrasound showed 5w5d based on measurements of the sac ) or she said maybe multiples ? What's your thoughts ladies I've never out of all 5 babies never had a quantitative this high this early mines were always 300 and below so I'm a little confused 😆 TIA for your response ☺️💗✨gen