.Most probably it looks like contact dermatitis or jock itch only. Hormonal changes during puberty,lifestyle and heredity each play a role in jock itch.
Most forms of jock itch respond to over-the-counter products, which contain any of several basic ingredients: miconazole, tolnaftate, terbinafine, and clotrimazole.
I feel that you should get it evaluated from a dermatologist as treatment for both contact dermatitis and jock itch is different and taking medicines on your own can aggravate the condition.
Hope it helps.Take care and pls do keep us posted if you have any additional queries