Why no positive OPK? Help!!!

I have been using OPKs every day since my last period ended, and I'm currently on CD 19 and still haven't gotten a positive test yet. (test from CD 16 is missing on the photo but was also negative) Some days I have tested twice and just once some days because I work alot. This is my first month using OPKs since I stopped on the pill a few months ago but my period has been regular ever since with 30 days in between periods.

Do you think I might have ovulated but just haven't caught it with a test?? My app says I'm 4 DPO