A couple of thoughts. You could try working your way into the hot/cold treatments. Start with the water not as hot or cold and only do a could rotations. Listen to your body, but realize that there will be obstacles and you will have to work into some things. Keep trying!
You can try a natural anti-fungal on the rash while you are working on the underlying cause. Garlic is a wonderful antifungal. Make up some garlic oil and apply it to the rash. Grapefruit Seed extract is also a good anti-fungal, but not as easily obtained as garlic. There is also Tea Tree oil. I have seen that at Wal-Mart. Just make sure you dilute them in a base oil.