How early in your pregnancy can you start to get morning sickness?

About a week ago, I took a positive pregnancy test. I figure that I'm somewhere between 2 and 3 weeks along, but I haven't made it to the doctor yet, so I don't know for sure. For the past three days I've felt extremely nauseous. I thought it was too early to be getting morning sickness, but my friend says it can start pretty early. Have I come down with something or is it really morning sickness?
Thanks.

The discovery health program had a new special on yesterday and said that the latest studies show that women can begin experiencing the first signs of pregnancy as early as eight days after conception. So congrats it is most likely morning sickness. And although it sucks let me give you some good news. Studies show that although they are unable to find a reason for the connection between morning sickness and the health of the baby…. numerous studies done show that women who experience morning sickness are twice as likely as those who don't to have a healthy baby.
Good luck.