Irregular menstrual bleeding, also known as oligomenorrhea, can occur due to several different causes, some of which are normal and not a cause for concern, while others warrant medical evaluation. With that in mind, here are some of the potential causes of irregular menstrual bleeding: • Birth control medications • Bleeding disorders • Breastfeeding • Cervical or endometrial cancer • Changes in diet or exercise habits • Endometriosis • Hyperthyroidism, which is an overactive thyroid, or hypothyroidism, which is an underactive thyroid • Pelvic inflammatory disease • Perimenopause, also known as pre-menopause • Pituitary gland disorders affecting hormonal balances • Polycystic ovary syndrome (PCOS) • Pregnancy or pregnancy complications • Premature ovarian insufficiency • Significant weight gain or loss, as well as eating disorders • Stress • Travel • Use of certain medications, such as anticoagulants (blood thinners) or steroids • Uterine fibroids