Is the “GLOW” app predicting it right??

Anantara

We are TTC since few months now and My Dr said to participate from day 11 - 16 of the month (day 11 including the start date of my periods).

When i entered my period dates in <a href="https://play.google.com/store/apps/details?id=com.glow.android">GLOW app</a>, it is predicting the 15-19 days as most fertile for me for this month. Am confused. Please help!!