Has anyone ever had this foot problem? Any podiatrists out there?

For about two months, I have had a swollen, painful left foot. It just started one day for no reason. I have been to a couple of family practice doctors and they do not know. An xray was taken, but it doesn't show anything. The pain and swelling is right on the top of the foot, between the toes and ankle area. I have not had the funds to see a specialist. What is really weird is that it is more painful while resting, and less while standing and walking. Any opinions would be appreciated. Thank you!