Hello Wot,
Based on your description you may have a condition called tinea versicolor. This is due to a fungal infection and is more common in hot and humid climates and in people who perspire more.
After a few weeks of treatment with antifungal creams, the infection may have resolved, but the residual hypopigmentation (white marks) can persist for a longer period, for months.
In such an instance, a fungal scraping or culture will help to determine whether there is still active fungus infection.
There are however a few other possible conditions that may look alike and you will probably need to visit your doctor for a proper examination.
