Some of my music purchases on my iPhone have disappeared after syncing to new iTunes?

I recently downloaded iTunes on my new laptop and synced my iPhone 5S.

About 5 purchased songs have disappeared. I went to iTunes and checked under 'purchased' but they were not there. Then I searched the songs and it is asking me to buy them. But I have already! I even found a list (like a receipt) of the music that I bought and they are there.

These songs are still on my other iPhone since I haven't synced that one yet. I checked iTunes on the iPhone that hasn't been synced and it also says I never bought them even though they're in my music library.

I assumed they might be 'hidden' but they are not.

What do I do?

Thank you so much!!!