Rash On The Bottom Of Butt Cheek, Starting To Spread Into Crack. Was In A Hot Place And Very Sweaty. Allergy / Infection ?

Hi Dr. Kondekar. I have been experiencing a rash on the bottom of my butt cheeks for close to a month now. It is starting to spread into the crack. I believed that it was due to a laundry soap allergy at first because I tend to be sensitive to those sorts of things, but it is not improving and I fear it may be due to a fungal infection after doing some research. Is this a common occurrence? I have been in the tropics of Central Kalimantan Borneo for the past four months where it is hot and often sweaty, but I did not ever notice an abundance of sweat there. I did sit often for long periods of time on the forest floor however... Any ideas?