Survivor since 2011
Sounds like it could certainly be the reason. Did you have radiation? I was fine after my mastectomy (also only one side with an expander) but since finishing radiation in July I have had trouble with tightness from the chest area throughout the shoulder and down my side. It's normal, but sometimes it may be hard to realize what you're feeling could be from rads. I totally agree with physical therapy and/or yoga. I do both and they help a lot!