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The descriptions provided is suggestive of a fungal infection
most probably due to unhygienic conditions or moist undergarments mostly due to excessive sweating
The Treatment recommended is to keep care of your hygiene including undergarments and skin as well. Topical anti-fungal like ketoconazole often available in combination with hydrocortisone
ointment and an antiallergic preferably loratidine or fexofenadine
for itch and rash symptoms.
All the drugs are on the counter available.