Minecraft won't load any worlds unless I delete it and then I lose all progress.

Minecraft on my IPad Mini has been having problems recently. It started refusing to load onto any sort of world a few days after I redownload it, and the only way to fix the lagging is to yet again delete and redownload it. It's extremely irritating and I (obviously) lose my progress, so please, either fix the lagging issue, or allow people to save their progress onto Xbox live accounts or I don't know. Just do something about it before I snap and crush my IPad mini.