From the description provided it could be related to a number of conditions, and in such cases (especially involving the skin), it is best not to self prescribe.
From the description this could be a simple rash
, etc. As I cannot visualize your presentation I would recommend a visit to the doctors office.
Taking into consideration the location, if it were a moisturization problem, it should have subsided by now. Also, the region where this has occurred is usually always quite moist and easily accumulates sweat and bacteria, which can result in an infection, if the region has broken or cracked skin. To avoid an infection, I would recommend and urgent visit to your doctor.
In the meantime, try to keep the region clean and dry. And wear loose and comfortable undergarments (preferably cotton) or avoid them completely to prevent friction.
Hope this helps..