OK, after a particularly uncomfortable 10 mile ride on a friend's mountain bike--I have to ask. Have you measured you sit bones? Are your sit bones on the seat? After toughing it out today on a bike that was too tall and too long for me with no bike shorts (at least I learned to stand and pedal more), I discovered it really was a too-narrow seat. Instead of resting on my sit bones, I was resting on my pubic bone. Just a thought.