HELP!!! I LOST ABOUT 200 SONGS FROM MY IPOD!!?

i added about 40 songs to my ipod before i went to bed on friday, and they were songs that my friend sent me over msn instant messenger. i woke up the next day (saturday) and 200 random songs were gone off my ipod. i cant find them on itunes either. the only songs that survived were the ones from the movie mamma mia (and im a huge fan. isn't that weird???) so anyway can anybody help?? i only have about 80 songs left on my ipod. how do i get back the other 200?? those were the best songs!! PLEASE HELP!!