Do I really have a deviated septum?

I sometimes breathe through my left and other times my right nostril. It alternates from time to time...I wonder if that's normal. Am I supposed to breathe through both nostrils at the same time? As for my nasal features I can't really tell if my nose is straight...well it's not perfectly symmetrical. If I want to correct my breathing is septoplasty the only remedial procedure?