Kettlebells work better than dumbbells for flyes. Because of the position of the resistance, the pecs are under load for a greater proportion of the range of motion.
With dumbbells, the muscle tension on the pecs is greatly reduced at about 60% of the range of motion. This can make the reps less effective, especially when you're using a method where you must maintain constant tension to create an occlusion effect.
Eating more and training more can get you pretty far. But if you’ve stopped making progress, it’s time to reassess and do things differently. Here’s what may be putting your gains on hold.