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Change in period pattern, having shorter and lighter periods, or missed periods could be suggestive of pregnancy (if you are sexually active), hormonal imbalances, thyroid hormone derangements, hypothalamic or pituitary hormone problems, stress and lifestyle changes, anemia etc.
Consider visiting your doctor/gynecologist for thorough examination and further investigations to confirm the cause for your absent periods and start you with treatment as indicated by your investigation results to help you get your periods back on track.
Take care.