The pain you are discribing does not appear to be sciatia but in fact a neuroma, a pain in the base of the toes. Index neuroma on this website. Thre has been lots of discussion. Generally a few ways to handle, make sure you ride with a cleat/pedal that has a wide platform, make sure the cleat is properly positioned, make sure your shoes are comfortable but not loose - you told want your foot rocking around inside the shoe, and wiggle your toes, alternate clipping right then left, rest your feet occasionally.