Hi,
Thanks for posting your query at DoctorSpring.com
From the description provided, it could either be contact dermatitis due to some irritant like soap, cream, savlon etc or yeast infection.
To treat the same, you may follow these suggestions after your doctor's consent-
Wash the area with plain water
Apply clotrimazole beclomethasone cream or you can mix any antifungal cream with a steroid cream and apply twice in a day.
Take tab levocetirizine 5mg orally once in a day
Dont apply oil, soap, savlon or any other medicine over affected area.
Avoid self stimulation or physical contact till the lesion resolves.
Hope this would help.

Take care