Hi,
The fact that an infection has been ruled out in your case, the most probable diagnosis is Lichen Simplex infection. This is a skin condition occurring from chronic irritation of the vulva. The symptoms are constant irritation, itching and skin rash. Due to the constant irritation, the skin in the vulvo-vaginal area becomes thick. The cause is sensitivity to an allergen in the form of detergent etc. The treatment is avoiding the causative allergen and a mild steroid ointment.
Read more here
Regards,
Dr. Gupta

