iTunes playing up again

Ok I recently switched from a windows hp to a macbook pro as a gift after my other laptop stopped working so I've forgotten how to get past some annoying things on itunes.

I have an Ipod 4th gen and I added my videos to my ipod and they all synced well ok but I added songs ,524 as I'm still transferring them over and so when I sync them into my Ipod Itunes sends a message saying I have no space when I have over 8gb left also Itunes states I have 5,000 photos when I only have 3000.

Whats going on?