Why are these guys talking about me?

This group of late twenties early thirties men keep observing, talking about me at my office. I don't know why. It makes me uncomfortable. I smiled at them once to be polite. Then one of the guys tried to make friends with me and I was polite but quietly reduced contact. Now everytime I come around they giggle and smile and punch each other. Lately it has turned into a weird quietness while I walk by their table at lunch. I've also heard them discuss the things I do long after I've done them. Like signing out a book. Trying to finish a quiz.
It's making me uncomfortable and self conscious and I have a lot of anxiety. Why won't they stop observing and discussing my actions?
Why are these guys talking about me?
Post Opinion