Q: Users deleted after reinstalling Yosemite in OS X Recovery

I just resinstalled my Macbook Pro's OS (Yosemite 10.10.5) using OS X Recovery because my laptop was being extremely slow and problematic. All I did was click on "Reinstall OS X" and signed in so that it could perform the download over the Internet. I was told that doing it this way would preserve all my user groups and files; it was supposed to simply reinstall the OS and not touch anything else.

But when it went through the whole process and I finally booted it up again, NONE of my old files/accounts were there... just a blank, completely fresh account that I had to name. I don't even remember the Recovery HD mode giving me the option to completely erase the hard drive. Is there a way to recover the old files and user accounts? All help is appreciated.