PHOTOS RANDOMLY DISAPPEARING

I just noticed a lot of my pictures are missing from my iPhone and iCloud. I am missing thousands of pictures from 2018 and back and can only see like 10 random pictures for the years prior to 2018. These are pictures I recently say on iPhone and now suddenly disappeared. Why is this ? I did not delete pictures certainly not so many, nor did I use the option to free storage. NO they are not hidden and NO they did not go to my deleted photos. I cannot see them online on iCloud either. Again these are pictures I looked at not even a month ago.