Cannot sync entire itunes library with ipod

I feel like I am in an endless battle with itunes. Hopefully someone here can help me finish it.

So a few weeks ago, randomly, itunes stopped recognizing my ipod touch. As suggested by people on this forum I selected the option of manually manging my music and was able to manually transfer the missing albums. However by doing this itunes decided to take all my other music except for some randomly selected albums off my ipod.

I continued to manually return all of the albums in itunes that were missing onto the ipod and everything appeared to be syncing normally. In the bar at the top all the songs I wanted to put on appeared to be transferred and the bar at the bottom that shows how much space is on the device was as it had been prior to all these problems (3.58 GB free). However when the sync was finished everything reverted to how it had been before and nothing new had been added to the ipod. The bar at the bottom reverted to 5.85 GB free. In addition a lot of the album artwork on the music that had previously been there had disappeared.

I have the newest versions of itunes on all my devices.

Please help- I'm one false 'syncing complete' message from throwing my computer out the window

Thanks in advance!