Why is my gs5 internal storage full?

[Android Central Question]

The internal storage on my gs5 almost completely fills up (16gb model) at least twice a year i have to factory reset it to clear it out, when i go to file manager to see what is filling it its always around 10-13gb of "other", all my pics, video, etc are stored on a 128gb sd card, its getting kind of ridiculous, i download lots of pics and vids but it's all stored on my sd, but like clockwork the internal storage fills up every 5 months or so.
Also i don't see an option to upload a screenshot here.