Ages 13 through 15 can be a very awkward time for a young man. Sometimes the saying .." all thumbs and feet.." usually accompanies this age groups description. Basically, you're probably experiencing some coordination problems, and all this is a natural part of growing up.
On the other hand, pain is not a feeling to ignore, nor is it a natural part of youth baseball in any manner shape or form. So, if you're determined to pitch, I would strongly recommend a pitching coach who has the experience of dealing with pitchers who have gone through some sort of rehab program. In fact, a pitching coach who has been part of rehab group or team, bringing pitchers back into the fold. These men and women know the process of dealing with a certain amount of discomfort -NOT PAIN - and they understand the process of assessing the methods and mythology of why your experiencing what you're going through.
As an alternative suggestion, and please don't take this personally, some players are not cut out to be pitchers. Whether it be the body's lack of continuity to sustain the demands, the overall physical makeup, or some other factor or combination of factors.
Your physical and mental demeanor is not something that I'm privileged to, so I would suggest a one-on-meeting with a pitching coach who can size up your particular situation and give you an honest assessment of what's-what. Also, don't forget to include your parents and any other family member who can be supportive of you.