Imagine you were a pregnant woman, a ways into your second trimester. You are not quite waddling yet, but there is a definite shuffle to your step. Its 400 degrees outside, so yes, you are "glowing" a bit and the heat is not helping the swelling of your ankles, which is currently rivaling the swelling in your belly (and thighs).
So, when you notice a few construction workers and delivery men staring you down, you don't take offense. No, you think, "well hey, maybe I've still got it!"
That is until you reach the restroom and get the first full-length mirror view you have had of yourself all day. Yeah, they aren't looking because they like what they see. They, and probably everyone else, is looking because your Big Fat Purple Granny Panties are on display for their viewing pleasure.
The lesson: Buy a full-length mirror and some thicker clothes (and ditch the purple panties).