Check, adjust, change, re-fit the following:
1. Seat height.
2. Seat tilt.
3. Reach to bars.
4. Vary position on bike...stand up! Sit up. Hills, accelerations, stop signs, railroad tracks, etc. are invitations to get your butt up off the seat and get some circulation flowing.
5. Try different shorts. I like thin chamois, myself. Thicker or thinner may work for you. Different chamois materials also yield different results against the skin, but I don't think that's going to affect your numb sensation.
As suggested, you might try a few new seats. There's a variety of sizes and styles out there like never before. SMP and their clones are different looking. Some swear by them and some swear at them. You'll never know what they do or don't do for YOUR riding unless you try one.
You don't mention mileage or experience or if this problem suddenly appeared out of no where. If a low miles rider, sometimes simply building up your time in the saddle cures the problem.
Last resort? See your doctor. You might have a prostate the size of a grapefruit.