Plainly said, you might not have any reoccuring themes. Most people do, so Archs tip is definitely worth a try, but nevertheless if you don't find anything you might not have anything (yet, that can change). The only reoccuring theme in my dreams are swimming baths, and I'm about to say WAS because the last time was several weeks ago, then again sometimes it has been months between these types of dreams. Also upon finding something you might keep in mind that something that reoccurs a few times might not necesserily be an reoccuring theme as it might be a temporal thing (such a temporal thing are currently C&C harvesters for me, for whatever reason).