This is something you should get looked at during your next visit. I had this happen in one spot after a year and a half with no problems and it turns out a piece of cement had dislodged and gotten stuck under my gum.
The ortho removed it and my gum went back to normal.
Be sure you're flossing really well back there, even though it's a real pain for the far back molars. I think the swelling might be indicative of something being where it shouldn't - food debris, cement debris, plaque, whatever.