As far as a “simple” solution, whatever you do you will have to do repeatedly until the infection is gone. Of course, you’d have to do the same with any over-the-counter medication as well.
Vinegar kills all sorts of fungus and mold (I think it actually destroys the spores). Soaking your feet in a solution of vinegar and water twice a day will do the trick. If you have open wounds and are concerned about pain, reduce the concentration of vinegar to water and increase it again until you have healed. Here’s a link. http://www.ehow.com/how_4602341_cure-cider-vinegar-natural-cure.html
I’ve also had excellent results using tea tree oil, but you will still have to put it everywhere you have the fungus. You will need to kill the unseen spores as well, so apply it on areas of the foot you don’t have it. Be sure to let it dry before putting on your socks.
I also suggest you wear cotton socks and sandals rather than shoes. If that’s not possible, wear cotton and switch out the socks a few times every day to keep your feet as dry as you can.