Join Date:Joined: Oct 2010
Lollipop doesn't come with the Google Now Launcher as the default. You'll need to install the Google Now Launcher from the playstore if you haven't already. After you install that, once you press the home key it should ask you which launcher you want to use. Make sure you choose the correct Google Now Launcher, select "Always" and you should be good to go.
If you have already installed the Google Now Launcher, I would suggest uninstalling it and then reinstalling it.