The only thing is, you have to remember that all these muscles are attached and can have an effect on each other. If one muscle is weak compared to the surrounding muscles, it can throw everything off balance and cause pain somewhere.
What I'm saying is, just because the pain is in your bicep does not mean it's not related to one of the rotator cuff muscles.
I had pain in my inner bicep too and after all the research I've done, I'm 95% sure it does have something to do with the rotator cuff, probably tendinitis. I've been doing a lot of different rotator cuff exercises and my arm is feeling much stronger after 2 weeks.
I hope to start throwing in a week or so to see how my arm reacts and if the pain is gone.