My 13 week old has a barky cough. it's not continual, just every once in a while. should i take him to the dr?

Not necessary: If there is no fever and only an ocassional cough barky or not i would not worry about it. If it increases or has fever see your doctor immediately.

Workup and Mgt: I agree that this may be a mild viral illness, which should resolve spontaneously. If it does not, and/or is associated with other symptoms such as respiratory distress, poor feeding, sweating, poor growth, then I would advise a further evaluation. This may include imaging studies of the airway.