Two songs I bought vanished?

I bought two songs on my ipod touch, and have been trying to sync it to my computer. It finally worked and I found three other songs I had bought swimming around in my itunes music library, but the other two are nowhere in sight... and now they've been wiped off every playlist I had them on in my ipod. According to my ping history, I DID buy them, but they don't seem to exist anywhere in my ipod or itunes or in any folders on my computer. Can someone help me?