I assume you bathe your feet every day and change your cotton socks daily, and in view of everything you've tried, it looks like you have an allegy, possibly dietary. Try removing various ingredients in your diet - sugar, salt, dairy produce (swop to soya milk) and give each one a couple of weeks, and see if that works. If all of that fails, ask your GP to refer you to a dermatoligist at the hospital - this is obviously something deeper than basic Athletes Foot, and needs proper assessment.