I received a tetanus Shot, now I cannot throw a ball, my arm is dead

I received a Tetanus shot 3 months ago. I was told I should have this shot to prevent "Whooping Cough". I agreed with the Doctor. I am a Baseball player (pitcher). Two weeks after the shot. I played in a baseball tournament. I  have played pro ball and throw mid 80's still at 56 years old. I could not throw the ball, a dead arm. I noticed a baseball size soft lump in my armpit. I went back to the Doctor who told me I must have injured my arm, but sent me to a specialist. He took xrays and did not see anything wrong. He had me push, pull in every direction. A cortisone shot was given. It has been 12 days. I still cannot throw the ball. Any ideas to help me through this.