What kind cutters do you use? As far as i know anything made of stainless steel should last a while, or you could try box-cutters if they're affordable to you, since they're made to be discarded in the short term. In regard to where to cut, I think that's highly dependend on the person. Everyone has different sensitivities. Some prefer cutting in 'safer' areas like the back of the fore arm, where there's less arteries and nerves (also less messy). Though, since you've been doing it for a while, you might not feel much there.