Arm pain due to pitching?

I've played baseball for almost 8 years, but last year my arm started bothering me. It's my shoulder but not the top, the side. I took baseball off for a bit and it didn't hurt at all, it just hurts when i throw. Any ideas? I'm really worried its something like a torn rotator cuff, but that would hurt all the time right? It's just on days i throw and days after it hurts.