Something you are using is sending notifications. So some app on the device is sending them. If you didn't set up notifications on any app, then you may have a virus, malware, bad app, etc., on the phone. I would suggest uninstalling anything you recently added. Then restart the phone. If that doesn't resolve it, then try starting up in "Safe Mode" and then check for viruses and malware. If anything is found, it would have to be removed to fix the problem. In the end, if none of the former works, you may have to do a "Hard Reset" of the device, however I would save that for a last resort option, as it will wipe all data on the phone.
To get into "Safe Mode" please do the following.
1. First turn off the phone.
2. Next press and hold "Power" until you see the manufacturers logo on the screen, then release the power button.
3. "Quickly" press "Volume Down" and hold it for few seconds until you see the message "Safe mode: ON" or something similar.
4. If you wanted disable it, simply repeat the steps above, and you should see "Safe Mode: OFF" rather than on.