First thing to do is make sure you have a current and complete backup of your hard drive. If you have a drive you can clone your boot drive to that would expedite the troubleshooting.
Now log into another user account and see if the problem persists there in Photos. (This tells us if the problem is limited to your user account or is system wide).
If still a problem from your account boot into Safe Mode (Use Safe Mode to isolate issues with your Mac) and check to see if the problem persists there. Reboot normally and check again.
NOTE: Safe Mode boot can take up to 10 minutes as it's doing some system cache cleaning, volume verifying and directory repairing.
Lastly, it may be time to make an appointment at the nearest Apple Genius Bar for a free diagnostic check. They may want to wipe the drive and reinstall a clean system to assure that there's no 3rd party software that could be causing the problem. So that's why you should have a current and complete backup before taking it in. If you go the clone route you can boot from the clone, and erase the laptops boot drive and clone back to it from the external drive.