Iphone 5s displays wrong storage amount
I have an iPhone 5s with 16 GB of space. When I go to usage, my phone says I have used about 11 GB of space, but when I add up all my apps I get around 7-8 GB. My phone also displays around 500 MB of free space when it should be a few GBs. I know ios usea a few Gigabytes but my 'used' amount does not add up. I cannot use itunes at the moment, but I may be able to use it soon so please give an answer involving all possible outcomes with itunes.
I am planning on getting the Iphone SE soon, so will the problem be fixed when I get it, or will the problem carry over when I restore from a backup?
iPhone 5s, iOS 10