What're the common causes of breathing problems?

Many... There are many, many causes of breathing problems. Some are related to the respiratory system (asthma, copd), others to the cardiac system (congestive heart failure). Some problems are due to infection (pneumonia) and others related to trauma (quadriplegia). There are congenital causes (cystic fibrosis) and some causes where the etiology is not known. There are so many causes so see your doctor!