It may well be irritation and simply changing your underwear style and using cornstarch powder (not talc) will relieve it.
Alternatly you may consider a yeast type infection. Dark places where we sweat sometimes allows our bodies natural yeast/fungus to grow-much like athlete's foot. If the above suggestion does not provide relief get
Lotrimin AF cream and follow the directions on the tube. Wash the area and change underwear 1-2 times daily. If it begins to burn or seem infected see a DR.
Good luck, and be well.
I hope my answer is helpful. If you have more questions, just ask! I am happy to help. If not, please click "accept" so I may receive credit for my work.
Positive feedback and a bonus is appreciated when you feel I've earned it. Thank you, Christy