tendonitos in the elbow

I play baseball, im 14. I am right handed and play shortstop for my AAU team.
I can’t play on my school team this year either. When I extend my arm, it pops on the underside of my elbow.
When I throw it hurts really bad on the inside. and I’ve had this for almost a year, and nothing seems to be working. I used to go to physical theropy but it didn’t do anything.
I NEED SOME HELP! also like a year and a half ago I had bad should pains then, and I couldnt play then either. and I went to P.T. for that too and that worked.
I think it is a combination from my shoulder pains cuasing my tendonitios.
My DOC made me get an MRI and he says that I have tendonitios, and he just keeps telling me to rest but I have rested for about a year and a half now, and I think there is something I can do to help it. but I don’t no what. thanks