Hey mama, yes super normal yan lalo na after CS, yung hormones mo pa lang settling talaga, lalo if breastfeeding ka pa rin kasi that can delay or make periods irregular pa for months! A few of us tried the calendar method din habang waiting for cycles to normalize and honestly napaka-hit or miss, especially if ang period mo pa fluctuating pa lang. Since naka-delay ka na ng 21 days and nag-negative ka ng tests, I'd say check with your OB just to rule out pregnancy or any hormonal stuff, better safe than sorry, especially since plano nyo talaga mag-second baby at gusto nyo alam kung saan kayo financially at health-wise. Pero don't stress too much, marami sa amin experienced this din after birth, walang problema!