For Some Time Now I've Had A Persistent And Chronic

For some time now I've had a persistent and chronic soreness or ache in my left shoulder. It is not really "pain" but definitely discomfort, more so when I wake from sleeping. Over the past few days it has spread to an ache in my arm, mostly in the bicep. It's much like the feeling after you've worked out and your arm is sore afterwards. This has not gone away and is there throughout the day and night. What could be causing this shoulder issue of mine?