From what you said, I take it that you are right-handed and play volleyball & probably other sports.
Consider this, how much tension do you put in your right-handed spikes on the ball?
How much tension is placed on the upper right side of your body. All right-handed activities could be placing tension on that side of your upper body.
Think about the "cross-over" connection that is unconsciously placed in the left hip area / lower left side of body...
Recommend pressure point massage to relieve the tension that's been unconsciously placed & accumulated over time. Seek balance in how things are being done.