Hi and welcome to HCM. Thank you for your querry.
It doesnt sound like STD
but this must be ruled out . some other disorders can cause it as well such as follciultis, allergy
reaction, irritation or sebaceus gland inflammation. YOu should do swab test to investigate the exact causative agent,but it seems like bacterial inection. if there is no discharge,pain while urinating or pain in lower abdomen you shouldnt be worried,this seems like only localized infection. keep this area clean and dry,it would heal spontaneously,if not you might need systemic antibiotic treatment. Wish you good health.