Arm pain in first innings | Nurtition and injury prevention | TopVelocity Baseball Forum

Hi Guys!
I'm having some trouble on the early innings of my outings. My pre-game routine is basically doing some sprints, stretching, throwing (sometimes long, sometimes not, depends on the day), some j-band work and 20 throws in the bullpen.
I'm a starting pitcher, and I usually go long into games, 7+ innings. But my problem is that I am feeling a lot of pain after I finish the first inning.
My first inning is usually my worst, in terms of command, velocity and effectiveness. After I get out of the field on the first inning, I sit on the bench and the pain on my lower biceps and lateral side of my arm is huge. When I get into the second inning, I have more command, and it doesnt hurt while I pitch. Only when I sit on the dugout. Third inning is better, and so on and so forth. My best inning, where I have my best stuff, is usually my last. When I am close to the 80/100 pitches range.
Has anyone experienced this? I am trying to figure out how to solve this, specially because as a starter I need good starts, but I can't get my head around it. I have changed my pre-game workout, I have modified my weekly routine, stretched more, etc. If anyone has experienced this and has some advice, I'd welcome it

Thanks!