AF used to run like clockwork but now...

I've been tracking my cycle for almost a year, and my cycle was always 27 days, my period lasted 5 days and it was always on time. But since DH and i started ttc my cycle has been way out of whack! Last month my period came 2 days early and lasteq1ad 4 days, this month it came 4 days early! It's making it difficult to tell when my fertile week is. I follow the fertile week that Glow gives me, but then my period came early and it shifted my week back, meaning that the time i was having the most sex during my "fertile week" all wrong!