Shoulder pain

If you pretty much woke up with it, then you simply laid wrong last night and that pain might last you a while. You also could have pulled a muscle by lifting something heavy or lifting something the wrong way. You could have cradled the phone for too long (some lift their shoulder when doing that which causes damage, others get neckpain, or pain in both areas.) Could be trauma, if you somehow got banged up. Sometimes there is no external bruising. Could be as simple as somebody hitting you on the shoulder for a greeting or pumping your arm too hard. Really there are many reasons as to why a shoulder can hurt, even disease. Just take it easy with that arm and shoulder, no heavy lifting. Put some heat on it. That'll take care of it in two or three days.

When shoulders are exposed to cold wind or lean on cold and hard things, we may get sore shoulders. or excessive labour or exercises.

all kinds of things could be the cause, you pulled a muscle, you slept on it, or sleep badly sitting in front the computer sloughed over, even a cold coming on or arthritis.