Started my period on 16th usually lasts around 4days.. its day 8 and its now turned to very light and cokoured brown?

May be normal: Irregularities in the duration of bleeding are usually normal variations. Normal duration is 3 to 7 days; the brownish color suggests older blood. Miscarriage should always be considered but usually bleeding is heavy. Changes in hormone levels, especially estrogen, are usually responsible but uterine fibroids, thickened uterine lining can contribute. If doesn't normalize, seek evaluation.