Hi there Rutu.
As i always say, sadly dermatology is a
visual field & as such, it is best to visit a
dermatologist (second one for another opinion) near you.
The condition you describe could be a simple
fungal infection called Pityriasis Versicolor.
This can be diagnosed by a simple test involving skin scraping & examination under a microscope using KOH (potassium hydroxide 10%).
The treatment can also involve an oral medication (has to be taken with a prescription) of
fluconazole 400mg as a single dose & topical
ketoconazole cream.
Do treat the fmites & undergarments et al in hot water, dry them well & iron out the creases for best results & recurrences.
Good Luck!
Dr Praveen Rodrigues MD
Dermatologist, Cosmetologist, Venereologist
Vikram Hospital, Bangalore