Oh gosh, sorry to hear. One reason this can happen for what seems like no reason is if you have a vaginal infection. Do you have any discharge, itching at all? For this type of diagnosis and to be treated, you need to see your doctor. Your clothing could actually be involved if you have an allergic reaction to it. Cotton undies are best. Weird one is that you could have extra testosterone. You might notice if you have that other things like you've gained weight, you have a bit of facial hair, acne, more hair on the face but lose some up on top, etc. It could have something to do with your pubic hair. A hair could be stuck. Look for an ingrown hair or issue like that. Bottom line though, you probably should run this by your doctor to resolve it. good luck!!