"Going back to the causes, most important are cerebral cortex, which hold hypothalamus and pituitary gland. Menstruation starts by a hormone secretion in the hypothalamus and pituitary called as GnRH hormone. Whenever there is a variation of these hormones there is a variation of estrogen and progesterone leading to irregular cycles. Stress doesn’t mean sleepless nights, emotional imbalance, psychological shock. Stress could be in the form of drug abuse, antipsychotic drugs or eating disorders like binge eating, stress eating, where you put on a lot of fat in the body or malnutrition where you are avoiding to eat. Stress can be due to excessive exercise. People have a lot of craving to zero size. Doing exercise that your body is not used to, excessive vigorous exercise, where you are losing a lot of body fat or putting on a lot of weight, where you have sedentary lifestyle, excessive weight gain. All these are related to a hypothalamus abnormality, where the GnRH hormone is reduced and because of this there is either stimulation or depression of these hormones which leads to irregular cycles"