Not all of my music is syncing from itunes onto IPod touch

I have over 2000 songs on my iTunes, but on my iPod touch it says I only have 1200 songs on there, all of the songs on my iTunes are saved onto my iCloud, but for some reason they aren't all synced onto my iPod touch - i got the iPod touch in December 2017 and set up the Apple music as well so any songs I download from there are fine - but there are songs that I have had on my iTunes for a lot longer that aren't appearing or not downloaded, I used to have an old iPod nano before this so a lot of the music isn't purchased through iTunes, but are downloaded, like YouTube converting etc. as I couldn't afford to keep buying everything - I spent hours making sure all of the songs on my laptop on iTunes were uploaded to my iCloud and there were no issues, I've tried plugging my iPod touch into my laptop and syncing that way to see if that does anything, I've reset my iPod as well but nothing is happening, is there something in place now that blocks anything that isn't downloaded or purchased via the Apple music or iTunes store from being played on it? As I have some that work, but more recent ones it comes up saying "item cannot be played/item not available" and it doesn't let me download them - if it no longer allowsthis then that's fine and I can have a clear out and delete some music and try and find them on apple music - I'm not a massive user of Apple products and only have the iPod touch, so apologies if this seems a bit confusing!