if ovulation does not occur regularly, the body does not send signals to the uterus to regulate menstruation. Stress, jet lag, lack of sleep and too much exercise can disrupt your hormonal balance and cause a change in your usual menstrual cycle.....it may occur in women who have anemia i.e low haemoglobin levels,diabetes or thyroid problems. It is also common in women with high levels of a protein called prolactin in their blood...it can be the side effects of certain drugs like oral contraceptives,antipsychotics,antiepileptics...it may be due to poly cystic ovarian disease as well... So I would suggest you to consult nearest gynecologists for detailed clinical examination and evaluation they will do the needful.

Please  read my blog on PCOS. Hope that helps.. It's not normal to have delayed period. If it happens on a regular basis, please work with a Doctor who understands hormones.