right shoulder pain

i have pain in my right shoulder sometimes moving to different parts of my right arm. the shoulder really hursts at night when I lay down to go to sleep, Its strange that when I lay on my left shouldr, the right shoulder hurts like the devil, but when I lye on the right shoulder, the pain is not hardle there. Its seems to be in the ball of the shoulder all the way to the arm pit. Sometimes I get a mild pain in the left shoulder but it comes and goes. Do you have any idea what this may be. I know i'm stressed, over weight, and have hight cholesterol, but my blood pressure is fine
Usually 127-130 over 70 - 80.  130/80 usually not that much.