How do I get the rest of my music back on my iphone?

Hello,

I just recently erased all my iPhone 4s (iOS 8.3 version) data. After I added icloud back into my phone, the music that I had came back onto my phone and all I had to do was download it from my phone, which I did. However, before I erased everything, I had 74 songs, but now I only have 58 songs. I went onto my iTunes account and noticed that songs which were on my iTunes account were not on my iPhone.

I think it might be because I erased everything and started over, but I'm not entirely sure because this hasn't happened to me before. I've bought songs from on my computer and on my phone. All of the songs are on my library, however, some of them won't allow me to move the songs I had to my music library for my iPhone. When I try, it gives me an error saying 'there are duplicates, do you want to skip or continue?' of the sort.

I'd very much appreciate help and insight on this.

Thank you.