Help please ?

Im a bit confused ... me and my partner of 5 years are now unactively trying for our 2nd child together in other words not trying and buying a load of pts and hoping and draining ourselfs into it kind of thing just taking a calm relaxed approach to it anyway ... my period normally is spot on to the day but last month it came over a week early and was soooo horrible and painful im just wondering with it being early would it change my ovulation date ? Im keeping track of ovulation in a way but today is only a 15% chance day yet im pretty sure i ovulated a few days back ie had cramping and a snotty clear discharge so that would make glows calculator out of whack ? Please help me how do you figure out this ? Lol !