You need to assess what's happened and figure out how to make it better though. You've tried your way, which is you waiting and hoping people would take care of you socially, but this is the result you got, you ate lunch quietly and nobody went out of their way to get to know you. Time for something different, you gotta talk. If you just show up and do nothing you just end up being someone out-of-place, how are they going to get to know you if you don't talk? Maybe they think you don't even want to talk to them, everyone is reading each other and there's always two sides to a coin. Be nice, talk a little, show off your personality, get people to like you. That's how it always works. What doesn't usually work is not trying.