Thanks for the query.
On reading your symptoms and closely looking at your picture attached with your query,we are of the opinion that this could be a fungal or tenia infection which looks chronic. The other cause could be extreme dryness that has led to a white patch, that could have been triggered off by a local trauma like a scratch over the area and collection of crusts on top of it in layers. The cause need not be sexually transmitted disease all the time.
Kindly consult a dermatologist for a local examination. Do not apply any lotions, creams or cosmetic solutions over the affected area. The doctor would advice an effective antifungal cream with a steroid base if needed. Some people could be allergic to nylon undergarments and bottoms and develoo such lesions. Avoid them and wear cotton ones instead. You may also take a diet rich in vitamin c and consume antioxidant and vitamin E supplements. Avoid exposure of the area to sunlight until complete healing.
Hope this helped.
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