A yeast infection is an overgrowth of yeast cells (a fungus) that are naturally present in the vagina. This is caused by a pH imbalance. Symptoms include itching or soreness in the vagina, sometimes pain or burning when you urinate or have sex. Some women also have a thick, clumpy, white discharge that has no odor and looks a little like cottage cheese. These symptoms are more likely to occur during the week before your menstrual period.