i don't know where you are from so i don't know if the climate is hot or cool. wear cotton clothes. especially undergarments. usually people with this have a lot of folds that can't get air. make sure these areas are cleaned properly. see a doctor. maybe he/she could give you a prescription for a topical antifungal+steroid, like nystatin+triamcinalone cream. i have this when it gets very hot outside. you could use an anti-fungal powder to keep you dry in those areas. if it is spreading to your back you really need to see a doctor.