What Could A Firm, Liquid-filled Lump Behind My Left Ear, Where I Wear My Hearing Aid, Indicate?

i noticed a lump behind my ear left side on the head, maybe 1 1/2 inches long and 1/2 inch wide about 1/4 inch high, firm but feels liquid filled, no pain, no discoloration, spongey to the touch. I wear hearing aid behind the ear and noticed it. Only on one side