Keeps turning on itself and won't stay on.

Screen comes on itself, I can swipe and go into anything, but after about 30 seconds, the screen goes blank and the back light will be on for a couple seconds, then nothing. This will go on and on whenever it feels like it if I don't power it off. It might do it every 5 mn for awhile or maybe a few times then not for a couple hrs again. Battery stays charged. Plz help, I can't afford a new one. This isn't very old.