Hi and welcome to HCM.
It can be just irritation or allergy
reaction but also a yeast infection as well.
YOu shukd furst keep it clean and dry. DOnt wesr clothes that provoke sweating.
You can apply some antifungal creams and see will it help. ALso is HSV
-2 infection possible,but just wait few days and see iwll there be progression .If yes, you should visit gynaecologist.Wish you good health.