I would guess a carbuncle which is also called a boil. They are very common in sweaty areas. They can also spread. Keep the area as clean as possible, make sure to also wash your hands. There is a soap you can buy at any drug store called Hibiclens. I was told it is basically surgical soap. I am guessing it would irritate private areas so be careful. I would tell your parents. If you get another one, I would definitely tell them and see a Dr. A Dr. should culture the infection to determine which antibiotics will be effective to kill the bacteria. If your general health is bad, abnormally tired or sore, see a dr. even if you don't have another sore.
I was eventually hospitalized with a staph infection which was misdiagnosed for over 6 months. The medication I was prescribed worked to improve how I felt but didn't eliminate the bacteria in my body.