Hello I share your concern, i will try to help you out in best possible way. Looking at your description this could be STI or infected ulcer may be due to trauma during masturbation I would like further informationto help you better Your age and relevant medical history like diabetes or other metabolic disease You should ask your doctor for few investigations to confirm the diagnosis like Urine culture and sensitivity test as well as pus culture of the discharge from the rash Apart from.this blood sugar fasting and post prandial and Blood for CBC and liver function test are also advisable. Maintain good hygiene Wash and clean it with antiseptic solution or soap You can apply mupirocin ointment externally. Use condom during sex Hope this answers your question please feel free to ask for more clarification Thanks and regards