Hi all, I am a medical student (not quite a doctor), but I thought that I would throw my two cents in. Uneducated or "lazy" vegetarians who are lacking some of the essential amino acids and other things like iron can get very sick if they are not eating the correct amounts or combinations. Most of the best combinations are intuitive (for example southwest food usually features some corn and beans. This combination covers all the essential amino acids that eating beans alone would not yield.) As long as you know what you are doing, a vegetarian lifestyle can be very healthy (most definitely better than bacon, coke, and twinkies). You may have to try a little harder and pay attention to what you are eating for a while, but after that it'll probably become second nature.
Your doctor may be worried that you do not know what you are doing if this is new to you. Instead of discouraging you, he should have gone through ways to make your vegetarian diet healthy. If you want to become a vegetarian and he is not supporting you, I would seek a different physician. You might try someone with a D.O degree instead of an M.D. Many people do not know the difference. I am a D.O student and we have all the same training and are fully licensed just like an M.D., however we are taught to think more holistically and our training includes more nutrition and alternative medical education. A D.O. may have more education and be more able to help support you in making the switch. (The average M.D. gets 6 hours of nutrition in 4 years of medical school, we talk about nutirion atleast once a week.)
You are all taking great steps in educating yourselves just by being reading a site like this and I applaud your efforts, whether it be for health, moral, or economic reasons.