also highly recommend Nivea Sensitive Post-Shave Balm for soothing the skin on your scalp after you shave.
I would listen to these guys. Might also want to try putting the can of gel in a sink of hot water to warm it up. I would encourage you to ditch the can stuff when you get the chance. Don't dry off your head after you get out of the shower. It really sounds like you have dense hair in the back instead of sensitive skin. Don't rush. Might want to put your shaving gel on your head and let it sit while you shave your face. Then rinse it off and apply fresh. Keep mixing it up. Try what these guys said too. You might not be an everyday shaver.