Bought song on iTunes on iPhone, sync'd to iTunes computer, now won't play on iPhone? I bought two albums today on my iPhone, on my Apple ID, downloaded them to the iPhone, I then sync'd the phone this afternoon. 

Now the albums will not show on my iPhone and it's saying that they're associated with a different Apple ID?

Which it can't be since I haven't changed it?
I think you should sign out of the appstore, then sign in again.
Then, don't use syncing, just re-download the songs from the Purchased section.