You're probably suffering from Tinea cruris and corporis (Ringworm).
So antifungal treatment, both oral and topical for minimum 1 month is required.
Also don't use any over the counter steroids/medicines. It may worsen it.
Next Steps
Consult with images.
Health Tips
Clean your clothes daily with antiseptic solutions.
Avoid sharing your towels with your partner.
Avoid contact with childrens.
Don't use Dettol/Savlon/Suthol on the area.
Don't scratch.
Wear loose fitting clothing.