Hello,
Form the symptoms it can be tinea versicolor. The other possibility is of idiopathic guttate hypomelanosis. Tinea versicolor is caused by a fungus that lives in the skin of almost all adults. Factors that can cause the fungus to become more visible include high humidity and immune or hormone abnormalities. Treatment involves topical and oral antifungal medicines.
Idiopathic guttate hypomelanosis is characterized by flat white spots found on the shins and forearms. It may also arise on other sun exposed areas including the face, neck and shoulders. Usually nothing is to be done except sun protection. Attempts to destroy the lesions may leave brown marks or larger white marks, which may look worse than the original condition. The other treatment options are cryotherapy, dermaabrasion, creams like tretinoin and topical steroids.
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.
Just curious..have you tried using an anti fungal cream? A dermatologist could take a scraping and probably identify the cause under a microscope..