IPHONE 6 MUSIC PROBLEM ON ITUNES * HELP*

I Have an iPhone 6 64gb and when I add phone to computer via usb and pull up iTunes.

Then I start making playlist folders and playlists under those folders and starting adding away.....( lots of music) then all of a sudden I go in playlist I added before and there's an " ! " mark and I check phone and there not in there.... it happens every time and it kills me that I have to keep doing it I wasted 2 hours with it.

AUTO SYNC is off, manually manage audio is checked, and I know it works because I look when I first added it and it was there and boom it all of sudden " !" adds to all my songs. NO im not moving the file location so I have no idea what it could be. I need help