I don't know how to explain it perfectly, but here I go:
Should you lead your arm motion with your elbow? Because I'm experiencing muuuch better control and velocity by doing this, and I think I'm not feeling pain like I was before doing it.
I have seen lots of pictures of Major League Pitchers and it seems like every pitcher do it.
Here are a couple of pics of Glavine (whom I think has great mechanics):
See what I mean? What I'm trying to say is to have the elbow in front of the forearm on your arm motion.
I'm gonna put some more photos of other pitchers doing this: