Can't listen to purchased music without Wi-Fi?

I recently purchased some songs from Itunes (I downloaded them from my Iphone 5s) and now I can't listen to them if I don't have Wi-Fi. I also recently updated my phone to ios8 if that makes any difference. This is never happened before, any suggestions?

I'm also having problems listening to my music with this iOS 8 update but the thing is I didn't purchase them, it's an app I got for free (before) but now with iOS 8 some songs play and some don't and the app keeps crashing… WHY?!