I Have A Lump That Feels To Be Around The

I have a lump that feels to be around the size slightly smaller than a quarter, inside my cheek by my back molars, but it cannot be felt from the inside of my mouth or seen from the outside, only felt when I touch it. I don't think I am sick or getting sick, and was told that the area I'm referring to is not a lymph node. What could this be?