HELP ME MAKE SCENES OF THIS PLEASE

I Have A 30 Day Cycle i start testing the day after my menstrual (flashing smiley face) all the way up to day 14 (solid smiley) ( on day 15 and 16 i use a dip stick and still BFP Ovulation) However this month on day 14 i got a BFP ovulation on day 14 next day, day 15 it was negative.... need help understanding.... thanks