From the symptoms, various possibilities are there. These include contact Dermatitis
, rash due to friction rub with clothes, Dermatitis
(atopic, contact, allergic),excessive sweating causing sweat Dermatitis
or balanitis(due to an underlying infection (bacterial and fungal as well as other organisms) .
You may try calamine lotion on the rash. You should also maintain hygiene and try to keep the area clean and dry, wear loose-fitting cotton clothing.