iPhone 8 laggs on iOS 11.2?

Just bought an iPhone 8 a week ago(64GB) and it seemed fine with 11.1.2 for a day, then came 11.2... It slowed down, but thats not the main problem. The main problem is lag. It lags devastatingly much: lags when I open multi-tasking, when I open an app, when I close an app. But the most annoying part is, it lags when scrolling in an app, and lags whenever I play a game. WHY APPLE? Isn’t A11 bionic the processor that’s supposed to take care of lag issues and bring gaming on iPhones to a whole new level? Furthermore sometimes I feel like the touchscreen is not working properly, it feels so hard to touch. Could somebody help me please? I’m really frustrated. And before anyone would ask, I’ve checked everyting, its not a fake iPhone, it has the camera quaility of all the other iPhones, great stereo speakers, and most importantly the Serial number is valid. So what to do guys?:/