Why do I get so much anxiety before I see a doctor?

Anxiety. Possible fear of being asked questions or given painful procedures or being told you have scary illness or that he/she can do nothing to help or is not sure of the problem, etc.
White coat fears. It's quite common to be fearful before seeing the doctor. We are all fearful of being told we are "sicker" or have a hidden affliction that is life threatening. Relax. Breathe deeply and you will pass your physical examination with the doctor with flying colors.