How Is Tendonitis Different From Tennis Elbow?

My arm has hurt since october... i have gone to two doctors and physical therapist and it still hurts. The first doctor said i had tendonitis and the second sent me to physical therapist who said i had tennis elbow but it still hurts. I am in marching band and believe that i hurt my arm when i fell backwards with my sousaphone. It hurts to move my fingers and it always hurts...