My entire game crashed

So I was playing on this one world that I had had for years but after the newest update it just started like breaking down I guess. If I was flying over the ocean too long with my elytra, the app would close. If I opened chests to fast the game would lag then close out. Most recently I made a potion of slow falling and left the brewing stand for my entire app to shut down. I regrettably did not take a screenshot but the screen said something like 'this world could not be opened right now, try using a copy of the world or try again later.' I did not have a copy of this world so I went with the other option, I closed it and went about business. I go back to the app a few minutes later and try to open said world but it wouldn't let me. I couldn't even try to make a copy of the world to use later. I then tried to turn off my phone and try again later but when my phone turned back on and I opened the app all of my worlds were gone, like, every world. I have been playing on pocket edition for a few years now and I had worked very hard on all my projects. I don't want to sound like I'm begging or pleading or being annoying in any way, I just want help or some kind of assistance in this issue because right now the app looks like I just downloaded it for the first time.