Hi, welcome to Healthcare Magic.
You are suffering from fungal infection
of the area known as Tinea cruris
and Tinea corporis
The best treatment is oral and topical treatment of antifungals for around 2 weeks period under advice of your doctor. The infection will vanish dramatically.
You should also maintain proper hygiene, meaning taking daily bath with soap, wearing cotton clothes, change your undergarments two times a day, maintain a dry environment to prevent growth of fungus. This will prevent recurrent/ further infection.
With best health wishes,
Dr Sanjay K Kanodia