In brief: Yes but messy. You can use monistat while you are on your period. However, it will be messy. Typically, symptoms of yeast infection tend to improve with the onset of menstrual period because of changes in ph. In brief: Yes but messy. You can use monistat while you are on your period. However, it will be messy. Typically, symptoms of yeast infection tend to improve with the onset of menstrual period because of changes in ph. 