My husband and I have been trying for three months. Last month was the first month I used an OPK and tested my BBT. Yesterday after 15 DP0 I got my BFP!! I O on the 3rd and yesterday was the 18th. So I figured I'm 15 days pregnant, however the Glow <a href="https://play.google.com/store/apps/details?id=com.glow.android.nurture">Nurture</a> app said 3 weeks...how can that be?