Missing songs from iPod and iTunes

I was on itunes once and noticed a song I had purchased a long while back had a buy button next to it, which I thought was weird since I bought the song, so I checked my list of songs and it wasn't there. I thought about it a bit later and thought of a song I hadn't heard play in a while so I checked my list and that song wasn't there either. I checked my itunes and they aren't listed there either. Unfortunately I have no idea when they could have went missing or if there are others. I'm not sure either what may have caused it, I know I didn't delete them, any song I try to delete stays in the list thanks to cloud anyway, I'd like to be able to get my songs back, I paid for them after all.

I also have a good handful of songs that are doubled in my ipod list...