Irregular menstruation can occur due to a broad range of potential causes, including stress and lifestyle factors as well as serious underlying medical conditions. As such, if you are experiencing irregular menstruation, it is essential to speak with your primary care doctor or obstetrician-gynecologist (OBGYN) about your issues so they can get to the bottom of it and either rule out serious medical issues or treat those issues if they are found to be the culprit. With that in mind, here are some of the possible causes of irregular menstruation: - Bleeding disorders - Dietary or exercise routine changes - Endometriosis - Hyperthyroidism, which is an overabundance of activity within the thyroid gland - Hypothyroidism, which is not enough activity within the thyroid gland - Pelvic inflammatory disease (PID) - Pituitary disorders cause a hormonal imbalance - Polycystic ovary syndrome (PCOS) - Pregnancy complications - Significant weight loss or gain - Use of certain medications, such as anticoagulants, which are blood-thinning medications, birth control pills, or steroids - Uterine fibroids or polyps