Well one major advantage of a Dr. is that they can do testing to see if you have things that you can't tell on your own.
A Dr. determined that I had salmonella. I probably would never have realized it on my own.
They also did ultrasound and colonoscopy to make sure I don't have more serious things that I could never know for sure I do not have on my own. I don't exactly know what these things are, but I for sure know I don't have colon cancer, some kind of tearing or something, they did biopsies, etc.