How much bodyfat are you carrying?
Shedding some pounds can reveal more definition.
If you need to add some size start doing dips – maybe as the second movement in your chest routine.
Try Gironda style – tuck your chin, maintain a concave bend in the front of the body from head to toe with feet out in front of you, flair the elbows way out, and go down nice and deep for a good stretch.
If you’re lucky enough to have V-shaped dipping bars, try a “knuckles-facing-each-other” grip for even greater chest involvement.