Sounds like you are saving multiple copies of your backup. It is a good strategy if you want to revert to data from previous date, but that doesn't matter with music collection because the data never changes, it just adds more.
So you just need a to backup music directory only, changed data only, not the whole thing each time.
I used to use Windows Backup for most jobs, it used to be very configurable. But in Vinta/Win they have made it foolproof, which means even idiots can use it, and it is worthless for any specific custom job. You can't specify a directory to backup, you can only specify backup my music files. Every music file on the PC gets backed up. Maybe you are using this now?
You might think about getting a real backup manager program. Something free and reliable. Then it will be easy to do what you want. I'll look around, but I'm sure others have favs.