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
Do treat the fmites & undergarments et al in hot water, dry them well & iron out the creases for best results & recurrences.
Dr Praveen Rodrigues MD
Dermatologist, Cosmetologist, Venereologist
Vikram Hospital, Bangalore