"Are you sure it's not twins?"

Maybe it's just me, maybe I'm overreacting, or maybe it's just the hormones.. I was at the store last night, checking out, and the cashier asked me how far along I was. I kindly said "14 weeks." acting shocked, with wide eyes, she replied "Oh, congratulations, but are you sure it's not twins?!" I immediately burst into tears because that comment made me feel SO huge..