I agree that you can work your way up to the hot/cold treatments. I have read about it being done with gradual introduction before.
For the fungal rash, you could try cayenne. Cayenne has great anti fungal properties and has been used on open wounds and the great thing, it doesn't burn! You will feel a feeling of warmth but I have never heard of it burning, it's even been used to pack open wounds to stop bleeding. You could try making a poultice and applying it to the area.
I've heard of using Pau d'arco and Goldenseal for fungal infections also. I don't know enough about those herbs though to direct you in their use.