IPhone :: ITunes Won't Load My Music Library Onto It

I was having some issues with my MacBook Pro and had to reset it as recommended by an apple tech. When I went to sync my iPhone afterward, a message came up saying that I needed to transfer the songs on my phone to my iTunes library or MacBook (can't remember exactly), or risk losing them - so I did. Ever since then however, iTunes will only load roughly 100 songs onto my iPhone, when it used to fill my phone right up. The songs in my library still play on my laptop no problem, so there is no issues with the songs themselves. I tried 'googling' a fix and found a suggestion restore my iPhone from backups, which I did and then my phone was finally syncing normally and filling up the entire phone. This sync was taking several hours however, and I went out for dinner and drinks during it and was surprised that it was still not quite finished syncing when I arrived home. Then a friend called and it was a bit of an emergency, so I took the call, but while I was on the phone the cord came loose from my MacBook and the entire sync session was ruined, and now it won't sync properly again even when I reset from a backup.

Info:iPhone 3GS