Shoulder/bicep pain when laying on side?

For the last few days, whenever i lay down on my side to go to bed, i have this sharp pain in my left shoulder to about half way down to my elbow. Doesn't matter which side I'm laying on. I work at a job where I'm constantly moving my shoulders, arms, & back, but I've been working there almost a year now & I've never had anything like this happen before. It doesn't really hurt much any other time, just when trying to lay on my side. Does anyone know what this could be?