What is that popping sound?

By the end of the day on Wednesday I had a large belly, which I chalked up to bloating. On Thursday morning I still had a large belly but Jay said it wasn't really that large. By this morning, Friday, I decided to wear one of my non-baggy, pre-pregnant sweaters and low and behold I look like a half fat person- half pregnant person. When I went to the doctor today she said "yup, looks like you have popped" and then felt my tummy and said that the uterus is now just below the belly button.

Today is 15 weeks 2 days according to the chart. The most recent ultrasound dates us at 14 weeks 6 days but I'm ignoring that because it adds 3 days to the due date and that is not allowed.