Hormonal Imbalances: Conditions like polycystic ovary syndrome (PCOS) can disrupt hormonal balance. Stress: High levels of stress can affect the hypothalamus, which regulates the menstrual cycle. Weight Fluctuations: Significant weight loss or gain can impact hormone levels and menstrual regularity. Medications: Certain medications, including birth control pills, can alter the cycle. Medical Conditions: Conditions like thyroid disorders and endometriosis can affect menstruation.