refer to how many weeks you are based on the date of your last period. in all the books when they say something like "morning sickness may start around 6 weeks", they mean from your last period.
like chase said, not everyone gets morning sickness and it's different for everyone.
you could feel sick 24/7, you could feel sick in the evening, you could throw up daily, you could just be nauseous without throwing up, you could just feel a little yucky...
i found that eating small snacks throughout the day helped a lot. if i got too hungry i felt disgusting.