Hi, I had this once when I got a virus and I needed to get some asthma-type meds to help. You should check with your doctor. Do you have a cold or anything? If not, I would say it's your nerves.
If your taking deep breaths in fear of not getting enough air i would say its anxiety. Stress can make you want to take deep breaths to though. I catch myself doing it whenever im having a frustrating day. Do you just take a deep breath every once in a while or are you actualy stopping to focus on breathing?