You may need to see your podiatrist for evaluation and treatment. In a difficult case of athletes foot (fungus) like yours, he or she may take a sample of your skin or nails to accurately diagnose your problem. They may prescribe a different medication than you have already used (be sure to bring a list of what you have tried and for how long).
Some other factors to consider:
Controlling the environment of your feet is very important. This means keeping them dry, wearing wicking socks (avoid cotton socks), and alternating shoes on a daily basis to allow them to dry out. You may also need an antiperspirant for your feet.
Keep in mind, if you are immunocompromised (if you have vascular disease, diabetes, HIV, on immunosuppressive drugs) this problem will be more difficult to control.