Have a metal plate on face from injury sustainedthree years ago. Last few months increase in facial pain. Now have hard knot on cheekbone- painful.

Infected plate. If the increased pain and swelling is in the area of the pain, the plate/screws may be infected. See an oral surgeon or ENT doctor for this problem.
See doctor. Could be an infection or scar tissue. See your doctor that put the plate in, or an ent.