Why have my cycles become irregualr?

Don't know. 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.
Hormone fluctuation? A doctor can check to look for a medical issue, if a woman has mild menstrual-related symptoms. Many women have some variation of mucus discharge, of periods, or a missed period on occasion. Some women feel normal after a few days, but others have bothersome symptoms and follow-up with a doctor. A pregnancy test can be done after a missed period, or 3 wks after sex, if worried about pregnancy.