Why is my phone unresponsive and my celullar turns to 3g

Okay about the screen unresponsive, its not like totally unresponsive Or freezing. Its like when I’m trying to move the joystick in games,i wouldn’t respond to my touch and I found the solution to it by lock and unlock the phone.But it just fixes the problem only for a few second.No im not using and screen protector and My hands are dry and clean. Is it just my screen problem?

The next problem I have is that when I play games (Pubg,fortnite,mobilelegend) my cellular from 4g turns to 3g. And if I exit the app my cellular turns it back to 4g for some reason. I’ve tried using different carriers before it still have the same problem.

Btw my phone is Iphone 6s