Hello,
One possibility for such a rash is chafing but if there is any history of any recent injury then infection of the area also needs to be ruled out. Wash the areas several times with fresh water. Do not use any cosmetic products at the sites. You can apply some calamine lotion at the rash as it will help in soothing the skin. Also wear cotton undergarments. Application of mild corticosteroid cream and oral antiinflammatories like ibuprofen/acetaminophen are also helpful. If the symptoms are severe then it will be best to consult a dermatologist.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
i have almost the same problem but with a few more details.. i recently learned that i have Hidradenitis suppurativa, it is a type of skin disease but do not worry, it's treatable!