When should you go to an OB/GYN?

We just found out we are pregnant a couple of days ago. My sister who is in another country told me that I should go to an OB/GYN already so the doc can give me vitamins and whatever I need for the pregnancy.

I just called one clinic and the secretary said that that particular doctor doesn't see patients until they are 8 weeks pregnant. Which is more than halfway through the first trimester already. I thought the first trimester was the time with the most risk therefore the very time needed for an assistance of a doctor.

When did you go to the doctor after a positive pregnancy test and if anyone can recommend a good OB/GYN. Thanks!