I recently added songs to iTunes

I recently added songs to iTunes on my computer and then synced my iPod touch. When the sync was complete, I charged the iPod using the wall charger. This morning, I updated the iPod software and went to play the music, skipping or cancelling the requests for me to set it up. I then went to play some the new songs recently added, and the songs wouldn't play. I remembered I was prompted to sign into iTunes and log into a WiFi network, so I went into my settings and did both. The new song began to play, so I turned off the Mobile Hotspot on my phone. The song abruptly stopped playing. I connected to my phone and was able to play the song again. Why must I be connected to WiFi in order to play the new songs? How can I play the new songs offline?