dermatitis, contact dermatitis or allergies. Use a mild cleanser with moisturizing properties like Cetaphil. Also use cotton clothes and change the clothes twice if there is any increased sweating
antihistaminics like Benadryl or Claritin can be taken. Applying calamine lotion also helps in soothing the skin.
If the symptoms persist then get an evaluation done by 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.