I go along with Malacoda on the pressure. The next time you shave consciously evaluate whether along with stretching you're increasing the pressure of the gizmo against the skin. Also, stretching can be too much of a good thing.
IOW, pulling the skin taut is what you want but not necessarilly as tight as it can possibly be pulled. I'm only guessing that you might be overdoing the pull beyond what is necessary but be concious of that too and it may help to just pull until comfortably taut.