I did have a fungal sinus infection for quite a while. The fungus in my sinuses was the most stubborn thing to get rid of, even more so than all of my other problems. Like I said, the only thing that finally worked was upping my vitamin C dosage to almost 20g/day, spread out. I took Now Foods brand, which is cheap if you buy it in the 500 capsule size. At one point I was also taking the Costco brand.
You also need to take a ton of beneficial bacteria to aid in acidifying your digestive tract and sinuses. Drink homemade kefir and eat homemade sauerkraut every day. Also take probiotics. Finally, bromelain (pineapple enzyme) is another good thing to take. It winds up in your blood then eventually sinuses where it eats through the mucus and fungus buildup.
I tried so many things for the sinus fungus, neti pots, anti-fungal wash, prescription anti-fungal meds, but it was C that finally did it. It still tries to creep back once in a while if I eat a ton of sugar, but NOWHERE NEAR how it was back in the bad old days.