How often are you changing blades? If your blade is dull you may be pushing down a little to much without realizing. And maybe invest in some pre shave oil or baby oil.
If you want to make your blades last longer (to get more uses out of them) clean them off and soak them in baby oil. A dull blade will lead to bumps every time. Also, after you shave, rub your head with an ice cube. It feels good, IMO and it closes the pores that can lead to bumps if left open too long. Good luck!
Bump patrol my be the answer to your problem.