Too much heavy flat bench has given me bursitis, a fluid build up in the joint space caused from overuse of the shoulder. It could also be tendonitis - the shoulder is a junction for lots of soft tissue. For example, if the pain is intense and localized at the anterior delt, it could be an irritation of the biceps tendon which connects there. For me, rest/ice/heat/compression, a focus on my incline and less flat bench has helped me. Warm up your shoulders EVERY lift and be sure that you are stretched well. Get plenty of vitamin C for your connective tissue, stay well hydrated and perhaps use a tri-flex supplement just in case it is a more bony related injury. HMB can help regenerate lost/damaged tisue as well. A little bit of deca does the job for me, just watch out when you cycle off because you can have a relapse of sorts once the effects wear off, especially if you do not adjust your activity accordingly. My bench is still over 4 hundo, so don't be afraid that a little bit of rest is going to take you out of the runnings... Good luck.