Do you use Chamois Butt'r? That will help your skin slip instead of stick to the shorts. I never wear anything under my biking shorts. (If I am having a period I use The Keeper).

It must be a really funny site when I garb up. I squeeze a liberal amount of Chamois Butt'r on my shorts and spread that around. Then put a little directly on the crouch/leg junction. Then slide the shorts up and say, "Oh GAG!" and make all sorts of funny faces until it warms up because that cold, slimy feeling just drives me nuts. However, I've not had any sores since. It is just that initial putting on of the shorts that makes me feel icky.

If you are sliding on the seat at least your shorts and skin won't tug on each other.