Help.. PLEASE

I’m new to ovulation tests, I thought they could help being I have an irregular period. So before I started taking the tests Glow said my ovulation date was the 18th. Then I scanned in my first ever ovulation test (purple test) & it changed the date to the 16th (today) then I took another ovulation test (white test), scanned it in & Glow said my ovulation date was yesterday, even though that ovulation test was negative. Am I doing something wrong? Should i keep taking the ovulation tests, even though glow said I ovulated yesterday? Please help.