Help me with my iTunes please?

I got a new iPod touch 6th gen here recently, and like any iPod I went to sync it to my library on my computer. I have a TON of music, like 4000 songs equal to 29GB between digital purchases from the iTunes Store and hard copy CD's and stuff, which is okay because I got the 128GB version iPod. But for some reason certain CDs don't get synced? Like for example I have 3 link in park CDs and they show up in my iTunes library ON MY COMPUTER, but I go to my library on the music app and only 1 of them show up. This is happening to like a 1/4th of my music entirely. That's a good couple hundred songs. And every time I sync it just gives me this error message saying something along the lines of could not sync "some song name" and 160+ other songs to your apple device, and it lets me click for details but all it is is the list of things it won't sync, nothing about why it won't sync them. Can anyone help me out here? Music is my life I listen wherever I go it's important to me to get this thing working.