I bought an iphone off ebay about a month ago it is 1.1.2 firmware fully unlocked and came as it is with installer and ssh on it so i dnt have any clue about unlocking/jailbreaking the iphone

anyway ive been using it for about a month absolutley fine, got it all modded just the way i like it everything set up perfectly and running well on 02 pay as you go
however ive just plugged my iphone into itunes to sync some more music to it where it told me that my space that was taken up with music 6.62GB is now classed as 'other' and therefore cannot sync my music too it as my music has now dissapeared, i really dont want to have to restore the iPhone through itunes as i dont know how to re-jailbreak/unlock it and i dnt want to loose all my exsiting mods/settings/data etc.

anybody have an solutions for how to resolve this?
if i could just free up that space that should be my music i can resync the songs but i dnt know why it says its being taken up