Q: Multiple apps not working on iPhone 5S

I've had my iPhone 5S for nearly a year. In the past few weeks, nearly all of my apps have stopped working. Mail either shuts down immediately, or deletes and downloads all of my email every couple of minutes (imagine receiving 2000 unopened email notifications... Every few minutes). Facebook, Messenger and Snapchat immediately close after opening - sometimes I'm asked to re-log in upon launch, and they'll work again as normal for a couple hours.. The only things that are currently working are Messages, Safari and Spotify.

I've had this issue in the past and updates/hard resets/reset all hasn't stopped the issue... In the past apps have started working again fine after a few weeks, but with no reason that I can see.

Has anyone else experienced this, or knows what else I can do?

Cheers