Unfortunately most doctors don't know a lot about nutrition because it's just not part of their training, so they won't be much help. (Their training focuses on diagnosis and treatment of illnesses.)
Vegan food is not necessarily health food because there are lots of vegan junk foods. Sugars and lots of oils are vegan too. There are lots of refined foods that are vegan too. (Oreo cookies, french fries, and potato chips are all vegan.) Animal products are not good for us, but other foods can also be unhealthy.
Try to make sure that you are eating lots of whole foods rather than refined and processed foods - and try to eat a lot of fruits and vegetables. If you have some vegan friends and they look healthy, ask them for some healthy and yummy recipes.
You might need a nutritionist or dietician to have a look at your diet and offer some ideas for making your diet healthier. Check also this website from vegan dietician Jack Norris: http://jacknorrisrd.com/ A lot of what you need to do is to learn how to replace unhealthy foods with new favourites.