Have Suffered A Pain In Upper Right Arm For Several

Have suffered a pain in upper right arm for several months, to stretch out or up and behind I get a stretching pain, there is no sign of any swelling or rash. When resting it feels like it is constantly aching. Have not taken any form of medicine as I thought this would have gone by now. I have not seen a doctor as of yet as I had hoped this was just a couple of weeks of strain. However I I still seem to suffer with this pain in my upper arm