Why do my legs get extremely itchy right after I shave?

I am 16 years old and been shaving for about 4 years now. I've never really had any irritation problems with shaving my legs until about 6 months ago. It's RIGHT after I shave my legs get so unbearably itchy. The first time it happened I rubbed ice all over my legs to numb them it was so bad. I also see little res spots covering some of my leg, this started with the itching. I do have sensitive skin, and I have tried using different tyoes of shaving creams for regular and sensitive skin, I have used soaps and seems now nothing works. I've been using the same brand of razor (venus embrace) for about 2 years now. Anyone know what may be the problem here besides to stop shaving, to wax, or use hair removal creams? (my skin overreacts with hair remval creams and waxing). PLease help!