I noticed it about 10-20 minutes ago. I'm sitting here playing guitar as im on the computer and every time i take my hand off the guitar i feel a slight ache near my right (im right handed so my picking hand) shoulder.
I think it is probably nothing but wanna be sure if anyone has had it before and wanna scream "STOP" before i continue XD
Its probably just simple fatigue but be sure to rest if your feeling more then very mild discomfort.
Guitarists tend to have the worst posture when playing, all slouched over and what not. A good rule is to do stretching warmups before playing if your having undue strain. Warming up your hands for playing is great, but alot of people neglect the other parts that are involved in playing. Like your shoulders.
Learning to keep all your muscles limber for playing is a big key to playing well.
Daniel