What Causes Pain In Left Arm When Putting It Up Or Sideways?

Hi, may I answer your health queries right now ? Please type your query here...hello. im 52 years old and almost everyday i do some light exercises at the office gym during lunch break. This has been going on for several months since mid last year and about a month ago im experiencing this pain on my left arm...esp. when i put my arm up and sideways. Im not sure what it is and what is causing this pain. I sometimes take Advil and it helps and sometimes i rub flexall and it helps but the pain doesn't go away. Can you tell me what this is or at least give me some idea on what it is that im experiencing? Thanks!