What Causes White Colour Discharge From Vagina?

hi i am 30 yr old i have three kids my priods was delayed for 6 weeks i had done pregnancy test several times was nagitive. then i take a medician norcolut for periods i take two tab each time for five days and then after finishing medician i have starting periods but first day there is white colour skin of 2 inches was on my pad. i am worried .what was that . thanks alina