Why the menstrual cyclo can be completely unregulated?

Hormone imbalance: There are many causes for irregular periods, most commonly it is from ovarian dysfunction and/or hormone imbalance.

Many reasons: Reasons for irregularity include weight gain or loss, breastfeeding, alcohol use, eating disorders, marked emotional stress, endometriosis, uterine fibroids, cervical polyps, polycystic ovarian syndrome, excessive exercise & pregnancy. When a girl has just started menstruating & around the time of menopause periods can be irregular.