Trouble adding music to playlist.

[Sturds]

Hello whenever I create a playlist on my Droid RAZR I can add all the songs I want to it but once its created I can't get it to add any new songs I've tried holding on a song and then selecting add to playlist and then the playlist and I've tried to open the playlist then hit menu then edit and it still won't add the news songs. It shows a message saying "__ number of songs added to playlist." ( __ being the number of songs). All of my music is saved to my internal storage also because whenever I ejected the SD card it would erase all my playlists. I am using the My Music app NOT the Play music app.