While running, try breathing through your mouth rather than the nose.

The mouth allows more oxygen to enter and more carbon dioxide to be released. If you attempt to breathe through your nose while running, your facial muscles will tighten and your jaw will have a tendency to clench. The act of breathing through your mouth will encourage your facial muscles to relax and therefore create a more relaxed composure. If you still feel you are out of breath Slow down a bit.