I discovered a lump on the back of my head last night. It is about the size of a quarter and is hard not moving. It is a little bit above my neck and centered. Could this be the cause of an infection or something else? If something else, what? Thanks. :)

Is it tender to the touch? I'm not an expert but it would help others to know if there is any pain or tenderness to the area. Could be a swollen lymph node fighting infection.