What Could Recurring White Itchy Patches On Lips Suggest?

I am having light white patch near my right side lips which some times causes itching. I consulted doctors they said it is nothing just caused by deficiendy of salts in the bodu and gave me medicine methico plus . For few of the days it was ok but now once agin at the same place I am seeing that patch with itching. Please help me wat is this?