When turning left or right, game becomes jittery.

When I load the game, and select a world, and start it, and start to play, when i turn left or right to place blocks, look around, walk, and run places, and get mobs, everything turns jittery, the whole time I'm playing, even if I restart it still does it, i cant seem to fix it. It happens sometimes if I open an old world then go into my main world. A world that I downloaded. Also when I leave the game and come back, and turn on the app without saving until I get back to the respawn point I came back, everything was totally black, I my character couldent see anything in the game, and the game said whatever the  players name is, died, but dident get hit with any mobs or anything, and all items gone. Its happend more than ones, I come back to the game,and sometimes it says that but where you could see everything normally tho, and when the game says that, it's in the voice in the game, not words, I have this computer voice tell me that on my phone I don't see how I may have messed anything up, also where it happend that's the new spawn point, and I know I dident save it there, Fix this please?