Depends where. External like armpits? Or gut? If it's external it is from excess fat and bad hygiene. If it's internal then maybe you need probiotics. Many autistic kids get yeast overgrowth in their gut, and so they go on an anti-candida diet. Anyways I guess you have been going to your doctor and getting medicine. If so, it is possible that the antibiotics are killing your good bacteria-oops.
Also you can ask your doctor what diet changes they recommend for preventing yeast infections. You can also Google what diet changes you can do.