assuming you did not strain or injure your arm i feel that it is related soley to your flu shot i think it important to address this issue with your doctor. sometimes the needle used for the injection can cause a hematoma -- a pocket of blood at the injection site. this can cause an sterile abscess or even an abscess that is secondarily infected. get it checked out.
two days after my flu shot my arm started aching. six weeks later and my arm still hurts. should i call my doctor?