I believe doctors in general are limited in their knowledge of vitamins. Do some research and find a vitamin brand that sounds good to you and then find a rep or visit a vitamin shop.
I am a Shaklee Distributor and I sell and take Shaklee vitamins. When someone contacts me I ask them what their goal is. What their health issues are, etc... and then make a recommendation. You can find someone like me or you could do your own research, decide what you need and go for it. Just be aware all supplements are not equal. Look for brands that are pure (tested for purity). Research your brand first. That should lead you to someone that can guide you for your personal needs.