My Son Keeps Getting Skin Fungus On Feet And Up

my son keeps getting skin fungus on feet and up his calve I took him to his doctor she prescribed ketoconazole and triamcinolone it worked for a week then he stopped for a week and on the third week it came back why? I minimize what he wears to bed because he had many layers prior to this for about 1 year he had this awful case of dandruff I would scratch it out have him wash his hair on his head but a day later it would look like mountains of dandruff his doctor prescribed nizoral shampoo. what can I do to change this re-occurrence.