Hi there I understand your concern...it may occur in women who have anemia i.e low haemoglobin levels,diabetes or thyroid problems...Stress, jet lag, lack of sleep and too much exercise can disrupt your hormonal balance and cause a change in your usual menstrual cycle...just consult nearest gynecologists for clinical examination they will do the needful.

If you  really  want  to  know  the root cause of your problem,  please  read my blogs on www.truhealing.com or practo health  feeds. Hope that helps....