every time I try to use the touch up tool in iphoto, it crashes

That's bad. I've seen some crashing lately when I use the Selective Color tool. Try re-starting in Safe Mode. This bypasses certain potentially disruptive processes. Safe Mode is different for different computers, so see this: 

           Start up your Mac in safe mode - Apple Support 

Also, is your Photos Library in the Pictures folder, or do you keep it on an external hard drive? If on an external drive, how is it formatted?

Do you use iCloud to sync your devices? Do you have "Optimize Storage" checked?

Have you used any system-wide apps, like disk cleaner-uppers? (Don't, by the way.)

If your library is in the Pictures folder do the following: as a test launch Photos with the Option key held down and create a new, test library.  Import some photos and test to see if the same problem persists. Does it? This tells us if the problem is limited to your current library or is more wide spread. Then open your current library and test again.