Hello dear Understand your concern Exact diagnosis made by examination and after proper investigation by consulting gynecologist. I think it is herpes infection, because of very sore and you had history of same before. Consult the dermatologist and get the done test for herpes like herpes simplex antigen and antibody by Elisa. Other causes may be immunological disorder like bullosimpetigo. Advice: Do not pop the blister it can cause infections After brusting you can wash with water and then Apply bandage till it heals Oral acyclovir tablet Apply acyclovir/valcyclovir ointment Also apply neomycin ointment to prevent infection You can also apply calamine lotion Tablet diclofenac Hope this may help you Best regards Dr. Sagar