Without seeing the lesion, it would be tough to say. I certainly would consider herpes. This can be further evaluated by taking a culture of the lesion, or doing a blood test to evaluate for herpes serology.
With any genital lesions, I would also test for other STDs, such as gonorrhea, chlamydia, and syphillis. A urinalysis to evaluate for UTI should also be considered.
If STDs have been ruled out, other possibilities would be dermatitis or a fungal infection. These can be treated with topical steroid creams or an anti-fungal cream respectively. You may want to consider a dermatology referral for further evaluation.
Followup with your personal physician is essential.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Kevin, M.D.
Medical Weblog:
kevinmd_b