I just assumed hormonal, but then I started getting twinges in my L shoulder, which turned into a dull aching and sometimes burning sensation. The area that it started out in was the side of the shoulder in the back, like under
the arm. Imagine lifting your arm up, and right beneath your armpit, you rub the vertical area underneath. Now, two months later, the pain has progressed to sometimes on the top of my arm, the muscle. I seem to notice it more when I'm at my desk working.