I'm 33 Years Old,weighing 73kgs And Has Been In Constant

I'm 33 years old,weighing 73kgs and has been in constant pain on my right upper arm for several months now..the pain feels like I've been punched really hard.i can lift my right aarm upward on standing tposition with minimal pain but with Moderate to sharp severe pain on sideways.sometimes,the pain radiates to my fingers and can be sometimes eased by stretching. I don't lift heavy weights so I don't know where I got it..I've been taking muscle relaxants and analgesics for a few days and still I'm having a hard time sleeping..just now my husband gave me amitriptyline for a change.i want to know the cause and what sleeping position could I possibly perform to ease the pain in the morning. No matter how I tried the pain cannot be ignored at night.Doing my ADL has been difficult like brushing my teeth or cutting meat with a knife :"(