Swollen gum around one tooth?

I have really good dental hygiene and brush/floss at least twice a day, everyday. I change my toothbrush often and even use mouthwash. For the last couple of days I noticed a swelling around one of my bottom molars, which is near the area where a wisdom tooth extraction happened about two years ago. It's not bleeding or *that* painful, really, but it's bothersome and more of a dull pain than anything (especially when I clench my teeth). Any ideas of what it could be? :(