My iPhone has 4.3 gigabytes used in photo library when I open the Settings, How do I get my memory back?

Why is this and how do I get my memory back? I got the Google Photos app and have uploaded all of my pictures to it and I have no pictures on my camera roll yet when I go to Settings -> Storage -> Manage storage -> my Photos app says I have used 4.3 gigabytes in my photo library can someone help me get my memory back? ( I'm on iOS 10 )

Is your deleted photos album empty?