How can I retrieve 2 years worth of photos from icloud?

I realized I am missing 2 years worth of photos from 2017 and 2018, because I see photos back to when I first got an Apple in 2014. I know I am missing them because my son was born in 2017 and I am **** sure I took lots of photos and I do not see them on my icloud. Same for 2018 photos are missing, I know I didn't go 2 years without backing up my phone because that is just asinine. Please any suggestions or help on how I can get these photos back and what could have possibly happened? thanks