With homeopathic medicines the amount of granules you take at any one time is largely irrelevant, what makes a difference is how often you take them, and the potency (ie 6ch or 30ch). So, unless you want to use your pack 5 times more quickly, then just take one. But 5 is ok too!
For something urgent, you can take the dose more often, for something chronic less often.
As it starts to get better you can decrease the frequency of the dose.
So for morning sickness, if you are taking nux vomica 6ch, you can take a granule when you start to feel rough, and perhaps repeat the dose an hour later. The remedy will work best if you don't take it at the same time as a meal.
If the morning sickness gets completely better, then stop taking all together (its not like antibiotics where you need to finish the course nor does it suppress your symptoms only for them to come back once you stop). You could see it as the nux vomica triggering your body to balance itself; once that has been done, you can stop taking it.
Although nux vomica is a useful remedy for morning sickness you may find that it doesn't work for you, and that some other remedy would. It could be useful to consult a trained homeopath in that instance.