I think when you have oral thrush they can do a culture for yeast, the same with a women because we have “discharge” with yeast. I think perhaps if you just have a rash and no discharge, there is nothing to culture.
I had this same problem with my lips. I had angular chelitis (which is caused by yeast), severe cracks in the corners of my mouth. But then I also had a lip rash that would cause my lips to swell and burn. When I asked if they could test my lips for yeast, they said that there was nothing they could culture and that they could do a punch biopsy. They tried to tell me that it couldn’t possibly be yeast. Idiots. Strangely, once I went on this diet and started doing antifungals, it started getting better….
Another little piece of advice my acupuncturist gave me, don’t wash with regular soap down there. Regular soaps have anti-bacterials in them that f#@k everything up with your flora and fauna so to speak. Find yourself some nice no-scent plain glycerin soap for after your workouts.