Screen Flicker's All The Time

Basically when I ever play minecraft pocket edition I get this lag attack ! It basically flickers the screen for ages and is so annoying can hardly play minecraft pocket edition like for example i was just going looking for mushrooms then I saw a creeper My screen flickers and the back ground freezes but continues then 20 seconds later the flickering stop's and I am dead ? Please fix this as it's very annoying and I can hard'ly play the game