Your nand backups are probably stored on your internal memory instead of your external sd card. That is usually the biggest culprit. Also, cloud storage also ends up on internal so that also could be the problem. Lastly, if you downloaded any movies from the watchon app they will install on internal unless you specify external.
Phones & Tablets: Galaxy S4, Galaxy Note 8", Evo 4g LTE, Evo 3D, Acer Iconia A500, Samsung Galaxy Tab 2 10.1, Ipad 2, Nabi 2,
Rom: Rooted Stock Odexed, Hotspot Mod, Xposed, Wanum