Help with iPhone screen issue?

Hey guys! I'm new here so sorry if I have messed up on anything in this post.

Anyways!

I got a second hand iPhone 4s from one of my dad's mates atleast 6 months ago. As soon as I got the phone, I came across an issue it had. The issue was, 'shaking'. Basically, let me elaborate, the screen shakes, like the top of the screen where it says the time and battery charge, is also at the bottom, its almost as if everything moves up. When I go in settings, a tab like 'General' would be in a row of 3 above the original tab because it is shaking so quickly 😐.However, this problem doesn't occur on everything. Apps (games) work fine, it's almost like applications that have a lot of words, and few colors on them get affected more. I have tried almost anything, the only way I can get it to stop shaking at all (slightly') is by turning on the setting 'Reduce White Point'. Hopefully it is not the GPU, and seeing as it does not affect games, I believe the GPU is fine. However, if anyone of you have seen, heard, or had this issue occur, and know how to fix this, or atleast stop the shaking, even if its just slightly, I would be greatly appreciated! Thankyou guys! 🙂