Hello I share your concern Looking at your description it seems to be caused by infection, Local allergy or an injury during sex or masterbation I would like more information.to help you better like Any history of exposure to unprotected sex? Relevant medical history like diabetes or other metabolic disorder ? In my opinion you should consult a dermatologist for physical examination and series of investigations to establish a diagnosis. You may require a course of antibiotics under supervision of your doctor Meanwhile wash it with antiseptic soap or solution and keep it moist by applying antibacterial ointment Maintain good hygiene Avoid sex or use condom until it heals completely Thanks for your question Wish you good health