My arm is in so much pain today!?

After a car accident 5 years ago and 2 surgeries later, my arm has a metal plate and screws from my elbow to my wrist and reinforcement around my wrist. Occasionally my arm will ache (when it's humid out) but nothing I can't deal with. Yesterday my arm started aching and feeling very heavy. It feels like it's swollen but it's not and it aches like never before :( and it kept me awake most of the night. My inclination is to just wait it out. Why does it hurt so much? (the accident was courtesy of a drunk driver)