My upper left arm pains when i use it since the last two weeks.the pain is continuous and is extensive but reduces after massaging but reappears again?

Muscle injury : Sounds like a muscle injury of some kind even if you don’t remember it happening- trauma, overuse, or even lying on it too long. Physical therapy or even some simple massage over a few days will help it to heal sooner. Inflammation is causing the pain and this situation can make the muscle tight and painful. So acetaminophen by mouth or muscle rub ointment may help the pain in the meantime.