iTunes Will Not Remove Songs When Syncing

I hope someone can help with this, as searching hasn't brought up any similar situations.

My iPhone 5s has been telling me that I'm almost out of storage. So, I decided I would clean it up a bit, remove some apps I never use, and some music that no longer suits my musical tastes right now. I also wanted to make a new playlist for my Apple Watch.

Here is how things went:

-Connected my phone to my Mac via USB and opened iTunes. Clicked on the little phone icon below the music controls.

-Selected 'Sync only checked songs and videos' on the summary page.

-Removed some apps (this went fine, the apps are no longer on my phone after synching)

-Went to music and de-selected all of the playlists, artists, and albums that I no longer want on my phone.

-Selected the music I do want.

-Clicked 'apply'.

No errors during synching, so I opened the music app on my phone to check that things were fine there and nope. Music that I wanted to be removed is still there, and music I wanted to add is not there.

I selected "Music" under "On My Device" and the list is very short and contains none of the music that is actually on the device.

I also went to my library, de-selected all, and selected only the artists I wanted to keep to see if this would change anything but it did not.

As a test, I de-selected Sync Music, which caused the storage bar to reflect the change. Then I clicked Sync, and the phone synched again, kept all the music I don't want it to keep, none of the music I do want it to keep, and the storage bar went back to the way it was reading before I de-selected music.

All of the music that is on there is music I have either purchased on my phone through iTunes on my phone, or redeemed as a Starbucks song of the week. I do not subscribe to iTunes Match. I do not use iCloud to backup my music.

I tried to select music again and sync the songs that I want and forget about removing what I don't want, and it doesn't even do that. Even the one single playlist that I made isn't syncing, but the phone has a playlist on it that has been deleted from my iTunes library.

I don't know what to do. ;_;

If anyone has any suggestions, I'm open...

iPhone is a 5s running iOS v8.4.1.

Using iTunes on a Macbook running Mac OS 10.10.5

iTunes is version 12.2.2.25