Pain in lateral deltoid

[karky]

Recently i have been noticing a pain in my lateral deltoyd. It comes mostly when i do the jerk part of the clean and jerk. Not if i just push press or military press something. I feel it also if i just move my arm around in a bit weird positiones, like doing external rotation (like when you are doing L-lat rises, and then on the top throw in an external rotation) it hurts at the end of the movement.
Could it be a flexibility issue? something i need a foam roller for? I so, could i use tennis balls, since thats the thing i got avelable right now.

Thanks in advance for any help!