Lost most of my photos

i share an icloud account with my mom and brother and when my phone isn’t on low power mode i get their photos and last night my phone got off low power mode and i got 20,000 photos ( all my brother’s ) so i would normally turn off icloud photos and turn it back on and get my photos, but that wasn’t the case this time. when i turned it back on all my brother’s photos went on mine camera roll and most of my photos were gone. i went to icloud photos and couldn’t find them anywhere, now i only have 171 of my photos instead of close to 2,000 photos. what should i do?