Thanks for your query.Based on the facts that you have posted it appears that you have Ringworm infection (Jack Itch)
Please apply topical anti fungal jelly like Meconazole twice daily.
Ensure to wash the entire area with warm water twice daily.
Ensure to wash your inner wares in boiling hot water mixed with antiseptic lotion like Dettol
I think with this treatment it will get cured within a week