ITunes For Mac :: Sync Is Only Two Steps Instead Of 4

Recently I have connected my phone to try and synchronise it because I had some new music that I would like to put on it. Unfortunately, when I connected and tried to sync I immediately found something odd because my sync did not do the full 4 steps but only 2, being : starting sync and looking for tracks to sync. 

I later discovered that for some odd reason iTunes said there was not enough space on my iPhone to sync my music with, even though there is over 10GB left of space. I read a similar problem where the iTunes wanted to re-sync the full library with the iPhone if it sensed that it was not the usual iPhone it did an initial sync with. However, that's not true. I am using the iPhone I've always used and this Mac's one and only hardware it's ever synced with is my iPhone. So I don't understand why iTunes would want to re-sync my full library. 

Furthermore, I only want to add around 20 soungs to my iPhone, which definitely does not take 10GB and the main issue is that without any recent updates or changes or anything, my sync only does two steps anymore and says there isn't enough capacity on my phone to sync it with. I unchecked "sync Music" to try and lower the space, pressed Apply but now it won't even sync my Music back anymore.

iPhone 4 iOS 7.0.2 version.