I believe the problem is similar to the problems with reinstalling Windows OS on your computer.
When you do a clean install, there is still various data floating around and now you have less memory until you delete that useless data.
Unfortunately you cannot do the same kind of thing that you can do with Windows (go in and just delete the useless folders).
I suggest you do a FULL wipe (not a handheld wipe), and then reinstall the OS.
I made a ton of videos about it; I suggest you go check them out and follow the instructions!
_________ YouTube - KillerNumberX's