Trying to conceive

Kalleen • Wanna have a baby
How do I know which <a href="https://play.google.com/store/apps/details?id=com.glow.android">ovulation apps</a> work an tell the truth cause I've tried three an they tell mi I'm ovulating on 28th which is glow an the other two said I was ovulating on the 29th an I'm fertile from 25th - 31... some help I'm confused