fungal infection not clearing up with medication

About a month ago my teenage son developed a rash on his stomach and several days latter a small patch appeared below his knee. The dermatologist cultured the rash and diagnosed it as a fungal infection. We have applied Ertaczo on a twice daily basis for almost 3 weeks and the rash is not going away. The rash begins to heal and then it breaks out all over again. The dermatologist wants to start him on week long course of Lamisil. My concerns are this:
1. Why is this not healing with the Ertaczo?
2. Could it be something else?
3. I'm concerned that Lamisil is a very powerful drug and he is a young boy?
4. Should I hold off on the Lamisil until I find out exactly what kind of fungus or what else the rash may be?
5. Would it be safe to try something like Tea Tree Oil or Black Walnut Oil that both have anti-fungal properties?
6. Do fungal infections normally take a long time to heal?
7. He also has a patch of hair on his scalp that has turned white (over six months ago) and the derm. said it was nothing. Now I'm concerned that there is something more systemic and serious going on

He is otherwise very healthy.
Thanks so much for any advice you can give me.....

[Dr Santos]

Hi,

Fungal infection usually responds to medical treatment. However, in some cases, it takes a long time before it completely heals. Diagnosis of fungal infection is through evaluation of the skin scrapings. If this turned out positive, it is a fungal infection, and nothing else, unless there is superimposed bacterial infection. Lamisil is usually safe with your son's age. It is important to keep the area clean and dry. Avoid touching or scratching to prevent spread and secondary infection. You can use alternative medication but discuss this with your doctor. He may prescribe you with alternative medications.

Take care and regards.