My gum behind my left molar is swollen, painful, and sore. What would this be from?

I had my wisdom teeth removed (they were impacted) in 2005. Behind my last molar the gum is swelling up and over the backside of the tooth. I cant completely touch my teeth as it pinches the bit of gum hanging over. The left side of my jaw is also tender around the area as well as underneath especially. Could this have been caused from my wisdom teeth getting pulled, or possibly something else? Any suggestions?