Help please

Okay so I've just come out of my fertile window 2 days ago I had intercourse right on time of ovulation  and the day after my fertile window had finished  I noticed pinkish blood on the tissue the next day it was brown in colour and very light and today it's brick red and heavy... I'm not due to start my period till the 21 of this month... Does anyone no what this could be... Very worried please help