Hi and welcome to HCM
You might have developed a
fungal infection in the area. They can be recurrent without treatment.
I would advise you to apply a plain antifungal cream twice daily, for atleast two weeks, like
terbinafine. If you have itching you can take an antihistamine like levocetrizine.
Apply the cream even if the
rash subsides for 2-3 weeks and then only stop.
Keep the area and all skin folds, and sweat prone areas always clean and dry. try to use comfortable cotton undergarments.
Also make sure your partner does not have any such infection as it can keep spreading.
If you see no change after this, then do consult a doctor and test the skin for fungus. Also rule out allergies to things like jewelry, metal fasteners, synthetic materials etc that maybe in constant contact with your skin in the area.
Hope this helps.