Are you a belly breather or chest breather. Put one hand on your chest and the other hand on your belly. Notice what hand rises when you inhale. Babies and relaxed individuals are belly breathers. Chest breathers may have had a trauma or traumas in their past that caused them to become chest breathers. There are many sites on the net that can teach you how to breath. This is a good one on how to.
This is a good one on how to expand your breathing: