It's definitely possible that you ovulated late if you're only tracking with an app. Apps only guess at when you will /have ovulate(D). There's literally no way for an app to know when you ovulate as ovulation can change based on so many factors. As you haven't tracked ovulation and it's ovulation that determines when your period would be due you don't even know whether your period is late.As long as you have continued having sex regularly throughout your cycle you still have a chance of being pregnant. Keep testing every few days until either you get your period or your bfp. Most docs won't see you until you've missed 2 whole periods.