Originally Posted by contango

If you have to keep shifting your weight back to the right spot look at your saddle position. Maybe you need to move it forwards or backwards, or change the tilt of it. If you do, make very small changes at a time. I once lowered my saddle about 1/4" and raised the nose by about 1/8" and it made a huge difference.

A long ride with a badly adjusted saddle may cause issues. I remember my first 200km ride caused me "comfort" issues that lasted a couple of days, but when I tweaked the saddle everything was fine.

If you're having gentlemanly issues several days after riding it might be worth seeing the doctor to make sure you haven't done more permanent damage.