ovulating late on a 28 day cycle?

Claudet • TTC #1
Hi gals! 
So I I'm cycle day 20. I thought I had ovulated on cycle day 16 because I got a positive OPK and I had the CM like raw egg whites, stretchy and all. 
I continued to take opks, even though " i had already ovulated".
But yesterday, cycle day 19 I got a positive also.
Did I ovulate late? Or why would I get a very positive OPK this late. 
Someone give advise, please 😩😩