What piece are you playing?
i had similar problems in a Villa-Lobos piece I played, though my glissando there was only going down.... Glissandi are best played with the thumbnail side of the hand, using swift motion from the elbow... going down you should play with the back of the thumb, and up with the back of 2,3,4,5... that's what I find easiest, and if you play lightly it doesn't hurt too much.... Toughen up....! be a man....