Q: Can't get all my music to download to itunes? Help Please!

I'm having a very difficult time trying to figure out how to get the music that I purchase on my iPad to sync into my iTunes on my computer.  I have the authorization on, I have it set to automatically update, and when I check for available downloads - the message states that iTunes has everything....yet I'm missing songs?  What am I missing here?  It looks like the only way I can get the music on my itunes on computer is to use the USB cord to load from my iPad but then all the apps download too and it takes waaaaaay too long.  I thought this was supposed to be easy?  Any advice would be greatly appreciated - thanks!!