is this a shoulder problem?

[ultrawaves]

when i do bench press and incline presses i feel a slight pain inside my armpit, awell as shoulder deep inside. but when i do should presses and other shoulder excerises i feel good, can someone tell me what type of injury i have, it just came out of nowhere, i didnt have any freak accidents and it doesnt bother me when im not working out....so can anyone tell me what kind of injury this is i know its minor but its irratating cause i dont wanna go heavy and injury myslef more

[-Nostalgia-]

Actually, that sounds like a back problem to me, or possibly a pulled/stressed tendon. How much do you bench?