Yeah, might be overtraining too.
Try to go for exercises that provide the greatest possible stretch and ROM.
A good Pec Dec machine is very valuable. I usually don't like machines, but heavy flyes kill my shoulder, and it's very hard to keep good form with them. Squeeze your pecs hard during the contraction and your chest will be screaming the next day.
Also try dips or weighted dips, with a good range of motion, lower yourself till your upper arms are parallel to ground and don't lock out at the top, which would allow your chest to rest. Lean forward, keep your elbows out, emphasizing the chest rather than the triceps.