Seems like you have developed a fungal infection
ie Tinea infection...Such infections usually occur in summers due to increased sweating and improper hygiene....Firstly avoid using any kind of oils or moisturising creams over the affected region....wear cotton clothes and undergarments...take bath daily ..You might need to apply a topical antifungal
cream (something like clotrimazole
gel) over the region for atleast 2 weeks.....And yes, weight loss
will definitely help in preventing the recurrence of such lesions..
Now as far as the pigmentation is concerned,,any infection or lesions over our skin heals with pigmentation....avoid itching as much as possible as it increases the chances of pigmentation....you may start takin some anti histamines
for itching as well,,,and yes,,once the infection heals up,,you can start treatment for pigmentation in the form of kojic acid creams...
Hope it helps
Dr Geetika Paul