I don't know if everyone gets these kind of cramps... During my periods, I have the gnawing kneading constant cramps AND I have a second kind, which sort of ramps up and then tapers off over 20-40 seconds (always less than a minute), and feels like it's happening in my bowels. During these cramps, I sort of rise up on the balls of my feet and hunch over in a desperate attempt to ease whatever is going on; I can't speak or do anything else til it passes. As I recall, unmedicated labor was like one of THOSE cramps, except instead of 20-40 seconds, and twice a day at most, it was 90 seconds-2 minutes, and happened over and over and over.
I can't speak to the actual childbirth part. After 18 hours of unproductive labor, they stuck an epidural in me and did a c-section. If I were ever to have another baby, I would not go through labor unmedicated. I don't know why I tried the first time.