Where does my iPhone storage go?

I have an 8Gb iPhone 5C, I don't use many apps except for music. I noticed that I had hardly any storage left so deleted any apps that I don't use, and It was only showing about 800MB of Music storage.

I decided to do a factory reset and then had access to over 4GB of space after reinstalling my apps.

Now after adding and removing various music albums and tracks from apple music, I seem to have used all my storage again. Deleted all music from the device and I only have 500MB of free space.

Storage screen currently shows

used 4.3Gb, available 805MB after deleting all emails

twitter 243mb

photos 219mb

instagram 215mb

and then 11 other apps all less than 60Mb

where am I using 4,3Gb of space?

I found that by doing a factory reset and then downloading as much music as I could it would store everything I want, but when I change the music I have stored I can never get back to having full memory available like after a reset.