Crashes, glitches and doesn't load!

For about a year now (maybe even more) Minecraft PE has been crashing and exiting automatically without me doing anything. I can't make a new world nor play a previous world. Neither can I play on servers. I don't know what to do anymore, it is really frustrating and I don't like thinking I've wasted my money because I know this should be a really good game! The game would sometimes work for a few minutes but it would be super glitchy, the world (land) wouldn't load and would just show blue 'sky's' and it would definitely crash a few minutes later but it's very unlikely for th world to stay in for more than 5 minutes! I really hope you fix this problem for I have played minecraft PE when it hadn't been crashing and it was an awful amount of fun but that was about two years ago! I hope this is in order. Thank you.