iPhone 5 Notification Error

When I am using my iPhone 5, alerts start to appear on my homescreen, it has happened three times already that a notification starts reappearing, even though I already saw the content, when I leave that certain app, it continues alerting me about the same thing over and over again, making my iPhone really slow. The only way to make it stop is by turing the phone off and turning it on again.

Please help!