Fungus

Antifungal creams or ointments:
These are typically the first line of treatment and can be bought over-the-counter.
Oral antifungal medications:
In some cases, a doctor may prescribe oral medications like fluconazole for more severe infections

Preventing recurrence:
Keeping the area clean and dry, using a barrier cream, and wearing loose clothing can help prevent future infections.

An established treatment for candida infections is miconazole cream. You can buy it over the counter, though you may need to look in the female remedies because it is often used for vaginal candidiasis infections. As Jeff notes, keeping the area clean and dry is important; some people use powder in the area to absorb any wetness that does occur.

Go and check with dermatologist IF it is a candida. There are different kinds of fungal infections that can inhabit our skin. You definitely need to keep area ultra dry.
Use tea-tree oil based soap, dry area and apply body powder (you can use any baby powder and there are also medicated body powders).
If you go to a gym take shower immediately, use your own towel ALWAYS, and apply powder and put on dry clothes.
Wear cotton underwear or shirts and wash them with bleach in hot water and use high heat for drying. You will have to start doing this even if you get real medications since once medication wears off you ca get fungal infection again if you do not take care of your skin.
Oral medications are extremely toxic to liver , so they should be your last resort.

Zot, how do you know its fungus ? You get it swabbed ? Especially that one ... I would keep area dry , use anti fungals ( creams) , and also get a Dr to take. look at it . There is some anti-fungal RX creams that work super well IF you know for certain it is fungus . I had fungus in the Philippines , down south while doing some training on circuits and approaches in Mindanao . Wa down there for 3 months , and picked up a nasty fungal infection . Went to Dr there and got a RX cream . two applications and it was gone , but I used it the full week as directed by Dr. . Worked great though . I kept the jar and used if for my feet . I still get to the Philippines yearly to see my friends there and relax . Some of the markets have home remedies for fungals that work really well too . Most of these home remedies at the market are like leaves made into paste and some sulfer or something mixed in . Its very common down there it appears . Hot weather and high humidity does it ! The soap down there I notice has some anti-fungals in it as well. One soap in particular I used to buy a lot cleaned your skin well and left your skin dry for a long time too !

derm doc looked and gave me nystatin, which after 4 weeks seems to have minimal effect, looking for alternatives

Try Ketoconazole cream 2.5% plus some hydrocortisone cream 2.5%.
Use a hair dryer to keep the area free of moisture and change your tee shirt often. Hope that helps…

Hmmmm, is you rash very vivid red with tiny bumps, or it is looking more like darker pigmented areas with lighter areas ? Any peeling ? To be honest candida is a yeast and as far as I know it rarely lives on top of the skin, mostly likes "cavities" and needs a lot of moisture. Perhaps it is not candida (yeast) but true fungus like Tinea so Nystatin in that case is too mild to have an effect. Derm. doctors are notoriously wrong with their assessments *sigh. I always tell my husband that I have no idea how dermatologists and meteorologists exist as a profession at all lol.