Wow, why would you use cortisone regularly? The rash is probably from sweating. Do you shower regularly? Using some corn starch there to prevent the sweating that is probably causing your problem in the armpits might save you some problems, as cortisone can cause a lot of problems. Mainly, at least in this post, you don't say why you think you have a yeast infection. Not to say it never happens, but men don't usually get them.