Ovulation tests

Hi, wondering if this has happened to someone before... I usually test for ovulation twice a day and even when positive I try again just to confirm... usually if I tested positive at night, it will still be positive in the morning and if I test again that same day in evening it will still test positive ... now, what happened was...I tested positive yesterday evening, this morning (although I knew I could use the opportunity because... work!!) and when I came back from work... negative! 😩