I have been dealing with the same issue here. The issue started around Christmas and continues to be an issue still today. Some days are better than others but from what I have found out up to this point is that I have a nasty knot in one of my back muscles that is on the medial side of my scap. I have had several ajustments from my chiro, a deep tissue message ( the kind you don’t fall asleep or relax during ha! ) and have had my athletic trainer from my college take a look at it. Today I will be going to an ART specialist, hopefully he can get something to loosen up.