Why do I have a bump on my jaw?

A few days ago, I got a cavity filled (w/o the numbing shot). Today, I noticed that I have a bump on my lower jaw (the cavity I had filled was on the top jaw) that hurts when I touch it and there is a constant discomfort. I asked my grandma, and she said it was probably drainage or something from the filling. I want to take her word for it, but I'm not sure. What could it be?