Don't listen to any of the above posts. I have a sure cure for your arm pain. What you do is go and get you 2 extra large binder clips. Place 1 clip in each hand and practice opening and closing them real fast. Once you have this down and are capable of of doing this 8 to 10 times in a row without any issues you hold 1 in each hand in the open position. At this time you close both eyes, reach up with both hands and clamp those clips to your ear lobes. No more arm pain.
Seriously, the best advice is to back off on whatever you are doing that is stressing your arm(s). Your pain is coming either from the muscle or the tendon. You have to rest your arm and allow it to heal. Some good advice, above.
Welcome to Chordie.
Nela