Hello,
It looks like fungal infection causing intertrigo. Application of local antifungal cream(terbinafine, clotrimazole, econazole, ketoconazole, miconazole) and oral antifungal drugs are the mainstay of treatment. Also wear cotton underwear and keep the skin as dry as possible.
You can consult a pharmacist and get any cream or lotion containing these ingredients. It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.