You should see a doctor. Chest pain when breathing deep can come from lots of different causes (some serious, some not) so you'll need a doc to figure out which one it is.
Injury to a rib like a bone bruise or fracture, inflammation where the ribs meet the sternum, asthma, allergies and bacterial or viral lung infections can cause chest pain from breathing.
If you have any shortness of breath or fever, get in to see your doctor right away or go to the ER. It might be pleurisy. (infection of the lung lining that often causes pain when breathing in)
