Ask What Else It Could Be
Another important question to bring up with your doctor is how he came to his diagnosis, and whether there are any other possible or likely conclusions as to what is wrong with your child. This is important because the pediatrician probably considered many different possibilities and concluded that it must be the most likely one. Other possibilities might not be out of the question, so it's good to get an idea of how sure the doctor is of his diagnosis.
This doesn't mean you should doubt the doctor's conclusion. It just means you should ask more about the other possibilities, why the doctor ruled them out and what to look for if the diagnosis does turn out to be wrong. Once you know the other things -- if there are any -- the doctor is considering, you'll be able to better watch out for those important symptoms.
However, considering their tight schedules, doctors might not have time to discuss the tell-tale signs of the other possibilities with you. So, instead, you can always try researching them on your own.