It is difficult confirming a diagnosis without examination but it can be sweat dermatitis, rash due to friction rub with clothes, contact dermatitis, heat rash or hives. 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 clothes. 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
I hope that helps. Take care and please do keep me posted on how you are doing or in case you have additional queries. Kind regards.