I have a small, swollen lump on the back of my head. It is tender to the touch or pillow. I have had no trauma to the area. Is this a concern?

Depends. If it is uncomfortable, you should go to doctor, it can be a cyst, and it might be infected or it can get infected, or it might be a lymph node and signify some kind of infection in the area. In any case it is better to take care of it earlier before it becomes a bigger problem.