Like aszala said, it could be a yest infection. Make an appointment with your ob-gyn. If she says it is a yeast infection, then she will give you something for it or you can go to the store and pick up some Monistat over the counter.
Many people are tempted to get the Monistat without going to the ob-gyn first, but you're exactly not supposed to do that. It is printed on the box that you need to go to the ob-gyn first. It can be dangerous to diagnose yourself and take medication for something you do not have, and yeast infection is not the only possible cause of itching.
As booy said, some people have itching due to certain condoms or spermicides.