Smartphone lagging when getting new messeges

[Roie Shalom]

When I'm about to get messeges, even half a minute before, the smartphone starts lagging ,on and off, what makes it really hard to write new messeges, as I have to wait until the phone gets out of this crazy situation. I've downloaded anti-virus and cleaning app, nothing helps. What cause this, and how to fix?

btw I'm not sure whether the phone acted like that when I bought it.