Can upper respiratory infection and bronchitis turn into pneumonia?

My son was diagnosed with upper respiratory infection on September 2, 2008 at the age of five months. Then on a follow-up visit on September 9, 2008 he was diagnosed with acute bronchitis. Then yet again on September 12, 2008 he was diagnosed with influenza. Then on September 25, 2008 he was diagnosed with pneumonia, after I took him to the emergency room after the doctor's office told me it was JUST a cold and he would be better by the following week. The doctor never once ordered a x-ray or checked his oxygen level, they just told me he was a Happy Wheezer and that he was fine.