Why did music disappear after syncing to Apple Music?

My dad has a family account on Apple Music so my siblings and I can use his account, but have our own music. I have never had any problems before but recently after signing into Apple TV with my dad’s account, all of my music got deleted. It really hurt because I had spent years making playlists and now they were gone. It said that to get my music back I had to “sync libraries” or something like that. So I did. I didn’t get my music back but I got all of my dad’s music on my phone. I unsynced my music hoping to just start a new library. But whenever I try to add music it says I have to sync again. I am just wondering if anyone can help me with this. I have searched the internet for solutions but no one seems to have the same problem as me. Anyone have any ideas as to how to fix this?

[Re-Titled by Moderator]