Hi
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Pain in mons and labial region could be due to infection. It may be STI. It may be due to poor hygiene during periods, tight underclothing,
injury during intercourse etc.. i suggest you to see a doctor for an examination , as you may need a dose of antibiotics,analgesics and local application as well , make sure you drink enough amount of water and do not irritate the mucosa , avoid soaps over the area and wear loose cotton under garments . Take care