I'm so confused!!!

Leah • ✨Leah✨PCOS 👣🌈 Angel baby 12-13-17 👶 Arianna Kaitlin 8-24-09💜 Engaged 💍 Rainbow baby due 11-21-2020 🌈

Okay so according to my LMP which was October 17th 2017, I should be 5 weeks 5 days today. The ER doctor is saying that my HCG levels and ultrasound are only measuring me just a little over 4 weeks. My levels were 6700, I'm so confused considering I got my BFP on November 13th... wth is going on!?