Everybody masturbates differently.
It is NORMAL for your glans, the head of your penis, to be very sensitive. Your foreskin has protected it your entire life. It's not used to being touched.
Can you retract your foreskin yet? Many guys can't until 16 or so but you can work on retracting your foreskin. Get an erection and pull down on the shaft skin so that the glans stretches the opening in your foreskin. Or, you can use your fingers to spread the opening. It might be easier to do in the shower, the warm water will help soften the skin. Take your time, don't force the foreskin back.
Hope it helps.