Severe Pain In Right Arm. What Can Be Done?

I am getting somewhat random sharp pains in the back of my upper right arm , between the elbow and shoulder , somewhat closer to the elbow. They have been gradually getting worse. It seems to occur when I extend my arm, though far from every time - it seems perhaps that it happens when my arm HASN T been extended fully for a while and then I extend it - though sometimes it seems to happen for no reason. It only lasts a few seconds, a minute at the most - and afterwards and also just at random times, I can extend for all I m worth and I won t feel a thing, no matter how hard I extend my arm. The pain fades after it hits until it s gone, it doesn t just suddenly vanish, but once it s gone theres no trace of it until the next time it occurs.