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Change in period pattern could be an early indication of onset of menopause. If you are sexually active (and not on any birth control measures), chances of pregnancy and implantation bleed also cannot be ruled out completely. Wait and watch for your next periods. If you suspect to be pregnant, look out for development of any other new symptoms suggestive of early pregnancy. If you are having other symptoms suggestive of menopausal onset, consider going ahead with visiting your doctor/gynecologist for examination and hormonal analysis to confirm/rule out menopausal onset.
Take care.