iPhone 5c Memory Issue

There is a weird bug on my iPhone 5c. I bought it about 6 months ago and it worked just fine for the first 5 months, but about a month ago it started flashing "Your storage/memory is full" massages.

The thing is there are about 2GBs of apps/photos stored on it which should leave another 3GB of free memory, but there is none. I thought I miscalculated something, but then again iTunes is also showing that I have 3GBs of free memory.

After reading a few post here I found out that a lot of people have the same issue. Turning off iCloud Drive seems to work for most people, but it didn't really work here.

I eventually did manage to get my memory/storage down to its normal state after restoring my phone from my last backup.

Sadly this lasted only for a week, before I got the same problem again..

Does anyone has any suggestions?