Ovulation Tests

Brittany • 34 years old;wife,mom, teacher
I am on day 15 of my cycle,and I have been doing an ovulation test, clear blue digital,every morning since Sunday. All of the tests are still saying not fertile (a circle). I still have a few more days to go and test and <a href="https://play.google.com/store/apps/details?id=com.glow.android">Glow app</a>/calendar says I will ovulate Sunday. Do you think I should be concerned?