Yes you need to be taking a vitamin! Not any special brand just a good womans health multi-vitamin and a folic acid supplement. We are 2 months preganant now and my wife isnt getting the regular prenatal because it has a tendancy to make her sick. As long as she has her womans "one-a-day" and an extra folic acid, she is doing great as well as the baby.
It is almost impossible to eat enough food in quantity and variety to feed you growing child and the last month of cook time is very imporant to how your child is going to be when he/she comes out. Sick or healthy, you are the only way that child can get thier food and oxygen.
Please get a multi-vitamin as soon as possible.