sounds like lymphodenopathy- a swelling of the lymph nodes behind your ear-
these nodes are part of your immune system and are only noticeable during an infection. the nodes usually pop up near the site of infection so if you have a sinus infection or ear/throat infeection this could be the cause. see a doctor to confirm and antibiotics and or cortisone would be helpful.
You need an immediate trip to an emergency room at a hospital for evaluation, unless you have a relationship with a physician who can see you today. This is not going to get better and the longer you delay in treatment the more the chances of serious complications. You may (a judgemental call) require hospitalization and intravenous antibiotics. Cortisone is contraindicated.
I also had a pee sized lump behind my ear, although I did not have the pain. Mine was a simple calcium deposit (hard as a rock). Because you have pain that may or may not be associated with this lump a call to your MD is highly recommended. The decision is yours.