I have a bad case of athlete's foot that I have received conventional treatment for. Now I think it has spread to one of my fingers.

Possible. What medication were you given? More than likely, it is difficult to spread to your fingers....Fungal infections Need warm, dark, moist environments to grow and live. The hands are not a good breeding ground. You possibly could have a bacterial infection which is possible or it may not be related. Try using Lamasil cream OTC for 2 weeks and see if that helps. If it gets worse, see your PCP.