Conversation with a Grocery Store Stranger

Stranger in checkout line: "You're having a boy, right?"
Me: "Nope, it's a girl"
SiL: "Really?!?"
Me: "Really"
SiL: "Are you sure?"
Me: "Yup"
SiL: "So you're in your last month, right?"
Me: "No, I have seven weeks left."
SiL: "Really?!?"
Me: "Yeah"
SiL: "That's a big baby"
Me: "Yup"
SiL: "Are you sure it's just one?"
Me: "Just one."
SiL: "Wow"

People have no clue.