i have the same thing and im 12!!!!!!!
Hello,
Without examination,confirmation of a diagnosis is tough but it can be contact dermatitis,rash due to friction rub with clothes,eczema,fungal infection,dermatitis (atopic, contact, allergic), heat rash or excessive sweating causing sweat dermatitis.
You may try calamine lotion on the rash. You should also maintain hygiene and try to keep the area clean and dry, wear loose-fitting cotton clothing. Also use an antibacterial soap or mild soap like dove.Avoid deodorant / cosmetics. You can also use a mild steroid cream on this rashAlso take some oral antihistaminics like Claritin if the rash itches.
If the rash persists then it will be best to get it evaluated from a dermatologist.
Hope it helps. Take care and pls do keep me posted on how you are doing or if you have any additional queries. Kind regards.