Iphone storage keeps on feeling up

I’ve had this problem for a while now, everytime i free up some space its full in less than an hour, when it gets to 200MB I can’t take any photos or read my emails it says “iPhone storage full” i once deleted everything in my phone just to be sure it kept on shrinking up to 190MB, i’ve had this problem since i was using the iPhone 5 every iphone i use it does the same thing, when i turn off the phone and on again i get like 100MB or so.