Could pain in my shoulder and down arm be caused from sleeping wrong on my side after BA?

I'm 4 months post op and about 3 weeks ago I started feeling pain down my arm and weakness in the use of my arm. No injury or reason I can recall that this would be causing discomfort... So I'm wondering if my sleeping on my side is causing this. I notice that I'm still not comfortable on my tummy, but I have always been a tummy or side sleeper. So I'm trying to position myself on my side, but cupping my arm to protect my boob.. Could this be causing my pain and if so any suggestions for relief?