Doctors are some of the smartest people around, but even they make mistakes after years of experience. Doctors often only have a short period (just 13 or so minutes!) to listen to you describe your symptoms the best you can before giving you a diagnosis, making it pretty easy for errors to occur.
I just want to tell you, I had a couple of close friends who were misdiagnosed and actually got sicker later on. If you want to be sure that your doctor is doing the right thing, I highly recommend you to click here to learn more about it!