The cause may be an infection, allergy, eczema, contact dermatitis or others like urinary tract infection.
For temporary relief you can wash the affected area with a glass of plain tap water mixed with a small spoon of salt or NORMAL SALINE(available in medical store).
Next Steps
You need to definitely consult a dermatologist/venereologist.
Health Tips
DON'T APPLY any cream/lotion by yourself or from medical store guy.
As some creams contain chemicals, steroids which will increase the problem and cause complication.
DON'T APPLY SOAP/BODY WASH GEL TO THE AFFECTED AREA. USE ONLY PLAIN TAP WATER TO CLEAN AFFECTED AREA.