Hi
Do you have a backup of your photos - that would be the normal way to recover from this sort of situation.
Where are you looking in your photos app? Are you looking in the all photos view? Also check the imports folder - that will show you everything that has been imported manually - even if they are misplaced in the all photos view.
How have you checked for a different photo library? You need to use the option start, as well as doing a spotlight search:
First try opening photos while holding the option key. Is more than one library listed. If so, open them in turn to see if any contain your photos.
If not, then use the spotlight search to see if there are any other libraries (search in finder). Put photoslibrary in the searchbox.
Make sure "this mac" is selected.
If you click on the found libraries in turn, the location will be shown at the bottom of the finder window. Open each one to see if they contain your images. (Use the option key to start photos then select the library)