I doubt its an std, dr. seems to think nothings wrong.

Could it be crabs?

Did your doctor suggest something like a jock itch spray?

Do you shave? This may seem like a weird question but the guys and girls who do shave in that region will attest (sp) to the fact that it itches when it begins to grow back.

If your doc says its all good then this is the only thing I can think of.

Could it be your soap? Have you changed brands lately? Soap has a tendency to remove all the natural oils from you skin and replace it with chemical moisterizers which can cause itching/allergies. Obviously you have to wash but try to limit how much you lather or rub/leave soap on skin and try to use tepid water instead of hot.