I had a very bad yeast infection in my groin area in 2010. Before going to see a dermatologist I put Desitin on it, worst thing you can possibly do, as yeast thrives on moisture and I don't believe the original formula Desitin has any antifungal ingredient. My dermatologist laughed at my attempt at self-help in this regard. My Dermatologist scraped samples off my skin and looked under a microscope at them and confirmed yeast infection in 30 seconds.
Anti-fungal creams we tried did not work. I finally had to get a prescription for Diflucan (antifungal pills), took a megadose once a week for 3 straight weeks, and it finally knocked it out. Took about a week after the 1st dose of Diflucan to notice improvement. In total between all the treatments I tried, it took 3-4 months to get rid of the yeast infection.
Keep the area dry if possible. The problem with the antifungal creams is they all contain water as an ingredient and when applied to the legpit area, the moisture is trapped in a dark area, and yeast thrive in such an environment. I think antifungal creams only work on yeast infections out in the open skin areas, and not in armpits, legpit or other body cavities or crevices.