What is the cause of having a period for 6 days when i always bleed for 5 days ?

Nature's not exact: Many women have occasional variation of their mucus discharge, some spotting between periods, a longer period, a shorter period, a heavier period, a lighter period, or even a missed period. Having one or two of these symptoms doesn’t necessarily mean there is a medical problem, but a visit to one’s primary care or Ob-Gyn doctor is a good idea if symptoms are persistent, recurring, or worrisome.