Confused!

Katy
Hi :) looking for some advice..... I was on the pill for 7 years after having my 1st child. I stopped taking it in feb and started ttc. My cycle has been regular 28 days untill this month..... It was 31 days..... U can imagine the excitement then dissapointment today! So im wondering now if my ovulation dates are off?! The app keeps changing dates so im confused. :/ when should i expect to ovulate this time if today is day 1?! Should i treat this nxt cycle as 28 days or 31...!??