I had this happen to me and it drove me CRAZY!!! I did some internet research and came up with the fact that this can happen to some people because of yeast (even without a vaginal yeast infection).
I started taking a product called "Yeast Cleanse" by Solaray (they sell it at the Vitamin Shoppe or vitaminshoppe.com). After a bit, the itching went away. Heavenly RELIEF. When I finished the bottle I stopped taking the pills, and unfortunately, the itch usually comes back after a while. I start taking the pills again, and the itch goes away, so I'm sure my self-diagnosis is correct. I find that once the itching stops I can cut the dose (3 tablets twice a day) in half (just take it once a day).
FYI, I remember that there was another, very serious condition with similar symptoms (though I don't remember the details), so if this (or the anti-fungal cream recommended by someone else) doesn't work, you should definitely have it checked out by a doctor.
Good luck!