Hi. Greetings. this could possibly be of frictional etiology if you are overweight or due to fungal infection. Fungal infection is quite common, especially more common in men/obese individuals, etc. This is often related to humidity, tight clothing, excess sweating and accumulation of moisture. You'll need to keep the area dry, wear lose clothing. You'll need to see a dermatologist for confirmation of infection and treatment with oral antifungals and creams. If there's resistance to one particular medicine another medicine may be needed depending on your improvement. DO NOT USE OVER THE COUNTER CREAMS LIKE BETNOVATE GM OR PAN DERM OR QUADRIDERM... this will only prolong the infection. You may Send further queries/ pics of lesions on private follow up chat.
Hope this helps.
Warm regards. Dr Govind S Mittal, Excel Care Hospital, Bangalore