Why do people make the comments they do?!?!

I am currently 16 weeks pregnant.. When I got pregnant I was the biggest I have ever been.. This is my 3rd and I started showing at 11 weeks.. Well lately people have been asking how far along I am... When I tell them they respond "are you having twins?" Ummm no there is only 1 in there.. Then they comment again "are you sure?? The second one could be hiding!" Pregnancy is a beautiful blessing and I am really trying to just roll with it but the way people judge and make comments is actually getting to me and I usually don't let that stuff bother me but lately it's getting me down!! A LOT of people make this comment to me it's not just a couple... Just wanted to vent!! Thanks for reading!! This is my 15 week bump!!