Contact the doctor who treated you in the hospital if you have not seen him outside the hospital yet. It was probably an orthopedic surgeon.
See a doctor. One possibility is you have an infection going on and your lymph nodes in your armpit are battling the infection. The swelling there could be causing your nerve pain, meaning it will go away when the lymph node swelling goes down, or it could be from the accident. Have the swelling looked at.