How to fix my iPhone 5c? It says low memory but there should be plenty of memory?

My usage claims I have 1GB free, iTunes claims I have over 2GB free. Both seem lower than they should be. I added up literally everything under usage (down to the 8 kb podcast app that I can't remove) and it only adds up to 1.8GB. I can only store 20 photos. I can't even update iOS (I have iOS 8.4.1, everything else is too big for my available memory). I installed iTunes because I thought I could fix it there but I can't seem to do anything on iTunes except look at what's on my phone. IIm very frustrated by this.

Added (1). Edited to add: I have 8 apps total installed. 7 of the apps are 300MB or less and the 8th is Facebook which is 636MB.

Added (2). Edited to add that per an internet suggestion I performed a hard reset (hold home and power until it reboots) and it only changed my available memory by 0.1 GB. Also before anyone suggests checking "Other" in iTunes, it is only 1.5 GB. Still Really need help!

Do an iCloud backup, then restore your phone through iTunes, and restore your iCloud backup to put everything back on… This will free up the cache and space your phone thinks s taken up