If you have already played with the seat position/height, type of seat and the reach to the bars I would say take a look at the shorts you are wearing. If there is a seam down the middle then that can very well be the culprit. Even some women specific shorts have a seam there just not on the chamois. Also, are you wearing your shorts commando style (no panties)? If not you should give that a try.

Also check out the Team Estrogen site as woodcycl suggested.

DBD