Apple iPhone help! Storage**?

Why do I have about 3.5 G of storage on my iPhone used up in the "Other" category?! I've tried everything to get rid of it. I've deleted all my old messages, deleted almost all my pictures and videos. I'm down to about 20 apps! I've searched the web many times but can't seem to be able to reclaim all that lost storage! If anyone can help 5 Stars!