If you're unable to view your news (activity about likes, Pins, etc.), you'll need to update your app. If you're using an Android phone/tablet or Nook, you can download the app from Google Play. If you're using a Kindle, download the app from Amazon. If you're using the app for iPad, iPhone or iPod, go to iTunes.
Once you have the most recent version of the app, you should start receiving notifications. Happy Pinning!