Why does Glow keep pushing my period back?

I was supposedly ovulating October 4 (my birthday) and I had sex the day before, the day of, and the day after. I took a test when I was 9 DPO which was a BFN, and I was supposed to get my period Friday the 20th (which never came). When I clicked "my period is late", glow pushed my period back 2 days to today. Still no period, so I clicked "my period is late" again and it pushed it back another 2 days. Should I retest? Im extremely confused.