How can I add a song to a playlist on my iPod?

Since I upgraded to iTunes 12, I can't seem to add a song from my music to a playlist on my iPod.

I tried two different ways:

1) Click on Music, then click on Playlists, and show Songs. Open up the iPod in the sidebar by twirling the arrow next to the iPod. I can add a song to the iPod by dragging it over iPod / Music, but I cannot add a song to a playlist by dragging it directly over the playlist name.

2) Click on iPod / Music. Try to drag the song from the iPod's music list to the iPod's playlist. Again, it won't let me.

So, how on earth do I add a song to a playlist???

Thanks