This can be difficult to do. Unfortunately, MD's are not above the typical prejudices we encounter from other anti-piercing people. Sometimes explaining your motivations for being pierced may help. Educating the educators, if you will. Remember, it's your body.
Doctors have legitimate concerns about the spread of infectious disease.
Just like you do. Explaining the methods you used to choose your piercer can help. Ask pierced friends and piercers for referrals. Piercing Guns can not be adequately sterilized and hurt more than a needle. The jewelry is suitable only for earlobes.