Everyone else has given GREAT advice! but here is a good solid stepping stone into doing some research.
http://pcrm.orgThe Physician's Committee For Responsible Medicine is a GROUP of doctors. When my rents were freaking out over my going VEGAN(a version of vegetarian where one eats NOTHING from an animal at all) and tried to shoot down PCRM, and I went to my next doctor, she RECOMMENDED this organization
My doctor also recommended Vegan.org and veggieteenscookbok.com
(And since my doctor recommended them and they ARE pro-vegan, they are bound to have PLENTY of reliable info. ;P)
Also, when you see your doctor, ask them where you can get some reliable information supporting a vegetarian diet over an omni one at any age.
Parent's are afraid to mess w/doctors, despite how little they actually know. ;P