It can be jock itch/fungal infection. U can try this
wash the affected skin two to three times a day.
Keep the affected area dry.
Avoid excess affected skin irritation by wearing 100% cotton underwear.
Avoid fabric softeners, bleaches, or harsh laundry detergents.
Wash your workout clothes, underwear, socks, and towels after each use.
Keep your affected area, inner thighs, and buttocks clean and dry, especially after you exercise and shower.
After showering or bathing, dry the irritated affected area by gently patting it with a towel. Be sure to dry your skin thoroughly.
Mix two tablespoons of apple cider vinegar in two cups of warm water. Wash the infected area with this solution and allow it to dry on its own. Another option is to apply a mixture of equal parts of white vinegar and coconut oil on the affected skin.
Like hydrogen peroxide, rubbing alcohol can help kill off the fungus that's on the surface level of the skin. You can apply it directly to the affected area
listerine: it has antiseptic, antifungal and antibacterial properties, which help treat skin problem
here are some tips to help you manage the infection:avoid using oily skin products.Reduce your exposure to the sun. Exposure to the sun may trigger or worsen an episode, do not wear tight clothing.
Wear breathable fabrics, such as cotton, to decrease sweating.
For this homeopathic treatment is very effective
for more details you can consult me.