Welcome to HealthcareMagic. From the symptoms it looks like the friction rub or chafing. The other possibility is of an allergic reaction
to the soaps, shower gel etc. Apply moisturizer and wear cotton undergarments. Application of mild corticosteroid cream and oral antiinflammatories like ibuprofen/acetaminophen
are also helpful. If the symptoms persist then consult a dermatologist
Hope it helps you. Regards.