odd cycle

my period cycle has always been very inconsistent. the only time it wasn't was when I was a teen on birth control. I download Glo back in September and have used it religiously trying to keep track of my cycle. It's been pretty accurate on my start day. maybe off by 2 or 3 days one way or the other. it said I was supposed to start on the 4th and here it is the 15th and still haven't started. wondering if I should take a pregnancy test. getting very anxious. would just like some opinions on how accurate yoh feel this app is and if maybe I should give it another week before freaking out lol