My period was due on the 25th July but was late by 9 days and didn't come until the 3rd August, on that day I started a contraceptive pill called cilest, which I was on before but stopped it about 4 months ago. When my period was late I took a pregnancy test which was negative which I was almost sure off because my boyfriend and I always have protected sex. My periods usually always last for 5 days but its now day 9. what could this be?