Thanks for a proper description.
This is most probably a condition called balanoposthitis.
This may appear due to unprotected sex or can just occur due to sudden exposure to hot and humid condition where you could not maintain personal hygiene well.
This is most of the times self limiting and just cleaning it 3-4 time with plain water and applying metronidazole cream can cure it within a few days.
if not cleared within 3 days, you may consult a Doctor to get a prescription foe and antibiotic and metronidazole orally.
Check for blood sugar.
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