Typically doing pushups will not give you any size increase or bulk that you want, however they will (obviously) increase your muscular stamina of your pecs. It is almost like running; doing a lot of running doesn't add bulk to your legs but obviously it increases your endurance.
I am not saying do not do pushups, but they will not give you the bulk that you would see from doing the typical benchpress, dumbell press, inclined press, etcetera.
Anyhow my advice would be to do as many pushups as you can until failure then go to your knees and keep doing them until failure. Do a couple of sets like that everyday and I think you will see some improvement over time.