I think the skin there must either be dry or irritated. The best thing you can do for now is to avoid over-cleansing or exfoliating that particular area. Make sure to properly moisture that area with a non-irritating moisturizer, and to use a hydrating essence/toner on it (not an astringent toner but a hydrating one). Hope this helps!

The rash is most likely caused by candida. Do you have a white coating on your tongue and/or have you taken antibiotics recently ? Oral or other systemic antibiotics cause candida breakouts on people's skin.

The treatment for candida rashes is topical anti-fungal cream. A cream with nystatin is the best. A cream with clotrimazole will also work. Do not moisturise the skin (apart from using the anti-fungal cream) because candida loves moisture. And do NOT use a moisturiser with organic oils in it (which means most moisturisers) because you might have malassezia, rather than candida (although candida is the most likely). Malassezia feeds on organic oils.

See my post in the tiny white plugs section of this site for more information.