I messed up my songs and got them deleted by a mistake?

So, I have downloaded and installed iOS 8 for my iPhone, and I get this idea that I want to get some new songs into my music "app" of my iPhone. I press Sync with entire library ( where i have pasted my songs) and lost my PREVIOUS songs and only have the new ones. Please note that my songs are not purchased through iTunes. How can I retrieve these songs back into my iPhone?

I don't think there's a way to retrieve them back besides redownloading them