It could be a yeast infection or a fungus. Try some anti-fungal soap and then see your doctor.
http://stevemark122000.hubpages.com/hub/How-to-Treat-and-Prevent-White-Patches-on-Skin
Could be vitiligo. Since this is an autoimmune disease, get tested for Celiac disease. If you test positive, not eating any gluten could stop other autoimmune diseases from popping up or even turn them around. I have had a turn around of an autoimmune disease (erythema nodosum) since stopping gluten. I have Celiac.