a 3" difference is pretty significant. Any medical reason for this? Childhood injuries, congenital issues, etc? Have you spoken to a doctor about that?

As was stated before, most people see size differences in the 1/4-1/2" range. I would say that it would even be somewhat difficult to detect a 1" difference. But I can understand why a 3" difference would cause you some discomfort. Still, I can't believe that this is simply an issue of having used a barbell for too long. My work is 95% barbell oriented and I can say that even with allowing for some "compensation" I have never experienced anything like what you are describing.