This can happen when you get run down from doing too much and not getting enough rest. Or it can happen as a result of illness. Repeated yeast infections can also be caused by other, less serious, illnesses or physical and mental stress. Some women get mild yeast infections towards the end of their menstrual periods, possibly in response to the body's hormonal changes. These mild infections sometimes go away without treatment as the menstrual cycle progresses.
Pregnant women are also more prone to develop yeast infections.
Sometimes hot, humid weather can make it easier for yeast infections to develop. And wearing layers of clothing in the winter that make you too warm indoors can also increase the likelihood of infection. But, she adds, they can be transmitted during sex. The best way not to have to worry about getting yeast infections this way is not to have sex. But if you do have sex, using a condom will help prevent transmission of yeast infections, just as it helps prevent transmission of more commonly sexually transmitted diseases, including HIV infection, and helps prevent pregnancy.