iPod won`t add songs.

K everythings been fine until a day or two ago. I go to plug in my ipod as usual and it asks for me to name my ipod and everything as if it was the first time it was being connected to the computer. so i named it and assumed everything was fine but then it sorta messed up the amount of space left on my ipod so it`s less now. I can only delete songs off my ipod now, not add them. it`s so confusing, this has never happened before. Oh and i`ve had this ipod for over a year. Please help, thanks.