Changed O day

Has anyone had their ovulation day changed in the app? Up until today, my ovulation day was supposed to be today but i just looked at it & now it says its on the 31st. Ive never had that happen in the 2 yrs ive been using this app. Ive been ttc since I miscarried last month. I was diagnosed with pcos since i was 16 & now im 39. My dr said he wanted me to try for a month & see what happens. For a week now ive been feeling nauseous & got sick on monday, some cramps but nothing like period pain cramps & have been bloated for a few days. Any ideas as to why the day would change?