Hello,I Am A 57 Year Old Woman And Lift Boxes

Hello,I am a 57 year old woman and lift boxes and unload trucks at work. I was told five years ago I had a degenerating spine. I have achiness and have been cut back on my artovastatin to see if it helps. I have pain in my shoulder blade on my right hand side,I am right handed ands pull a pallot jack with this arm. The thing I am concerned with is the pain is raidiating to my breast I think. Could thirs be a pulled muscle.