If you're not getting notifications that you expect to be receiving, their might be an issue with your notification preferences.

You can change your preferences by clicking your user icon, in the top right and selecting preferences. 

Under User Account you will see many options including Forum preferences, Message preferences and Notification preferences.

Check that the notification you expect to be receiving is checked for the method of reception you desire.

Also check that the source of the notification is configured to send them. For instance you must be subscribed to a forum to receive notifications. If you are not receiving them then you may not be subscribed.