The music I bought on my iphone 4s will not sync to my itunes.

I have an Iphone 4s that I got last summer and recently it has not synced any of my music (which I bought on my iphone) to my itunes. I have never had this problem before, and most forumns show a problem with syncing to an iphone. Furthermore, my account does not show the purchases I have made either. What do I do?