Ovulation test

Amanda • Married 6 yrs. Have 1 son. 1 daughter in heaven... She passed from SIDS 5/21/13-6/9/13. Now TTC #3 (our rainbow baby)
Need some help... Kinda new to the ovulation kits. I've been taking the digital clear blue easy test strips each morning for a little over a week now and I've been getting a "low" (circle) fertility. -Glow says I'm ovulating-- anyway, today on my way home from work I had a thought- I decided to come home and test (even though I had a low fertility test this a.m). So now, it shows the smily face (high fertility)! How did it go from low to high in less that 12 hrs? Like I completely skipped over the "peak fertility".... So confused 😩 Thoughts?