Hi,
My son gets this very often and has since he was little. I took him to a gastrologist and he said he has yeast overgrowth. Very common in boys. We haven't gotten rid of it completely some kids always have it. What has worked for me is keeping his diet low in products containing yeast and high in good yeast, like yogurt or go to herb store and buy capsules of it to put in his food. Adding the good yeast helps get rid of the bad yeast. Secondly I use Gentian Violet a natural herb you get from the pharmacy and swab the area 2 times a day for 4 days. Watch out its purple and does stain. sometimes these funguses live in the mouth and can go unseen, so swab a little around his gums also. You can check with the pharmacist its and old remedy my grandma and my mom used. Hope this helps.
If you've used anti-fungals for nine days and there is no change in his condition, you need to change treatments.
In my experience, anti-fungals work very quickly. It sounds like they need to culture whatever this is and figure it out, and switch your medications.
Best wishes.