Be sure to wash the area thoroughly while in the shower. Also try using a medicated powder like Gold Bond on the area after you get out of the shower and dry off. Also wear cotton underwear. When sweat and moisture gets trapped bacteria breeds and you end up with your problem. So you just need to prevent that from happening.
That doesn't appear to be normal. I know it's embarrassing, but have you considered talking to a doctor about it? Especially since it's causing pain.
When has this started? Perhaps you made some changes such as wearing a different type of underwear that contains materials you are allergic to. If you can find out the cause and eliminate it, that would be the most efficient solution. I have sensitive skin myself so I always have to watch what I put into contact with my skin.
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