How to fix my shoulder

Hey there,
I'm new to the whole workout scene, I usually go to the gym with my buddy, his goal has always been mass building and he knows what he's talking about and understands the movements and things.
A few weeks ago I went without him because I had to work or something. So I ended up working on my chest, I was on the flat bench. I ended up trying to push more then I should have and I think I rolled my shoulder (it hurt like a cheating ex-girlfriend!) I ended up taking the rest of the week off. Now I find that when ever I try to do chest workouts I get a sharp pain in that shoulder. I haven't push heavy in a while. it only hurts with certain motions. such as bench presses and flyes. I have no pain when not doing these excerises. I just finished with my back workout and didn't notice any pain. I don't over train. but I need to improve my nutrition. I work out 4 days a week back on Monday and chest on Tuesday, Wednesday off, Shoulders on Thursday and Arms on Friday, weekends off. I also notice this pain when I do some shoulders like the Arnold press.
well any feed back would be great on how to improve my shoulder. it really pisses me off when I struggle to press 30lbs (thats in total... I really want to improve my bench press)

Well thanks

Chris