help?

Was abit gutted when I found out my period started yesterday, me and my partner tried so hard to make it happen. AF is always due on the 21st of every month and mine was 3 days late, then AF happened yesterday. It started with pinkish/brownish colour, then bam it just come at once. I wasn't under any stress or on medication or anything, so was just wondering why it might of been late? Is it possible to still be pregnant and have a late period? I've had to readjust my glow calendar to when AF started😭