iPhone5 S 32GB has 20 GB taken by the 'other' category. I don't know how to fix this.

The other day I had virtually no other category. Now.... my phone is full. It warned me so when I woke up this morning! What on earth could have happened between now and just a couple of days ago?

I'm already aware that mail and messages can play a huge role in this. I guarantee both of those things are clean and not causing this problem.

In the past, with my iPhone4, I know that restoring then backing up would fix this problem (for me at least, anyway), but I feel sensitive to the things I have on my phone and I don't want to lose anything through a restoration. That's just paranoia talking. If it's universally agreed that I can fix the issue through a restore and back up, then I'll follow through with it.

I also know sometimes apps can be a problem.

Apps that I use often: CaltrainMe, Facebook, Facebook Messenger, Google Maps, Google Sheets, Puzzle & Dragons, Soundcloud, Spotify, Trillian, Tumblr, Youtube, Instagram, Snapchat, and a couple more that I want to keep disclosed but I feel aren't an issue.

Thank you. Here's a picture of the tragedy.