There are many potential causes of vomiting such as an infection (stomach flu), food poisioning, electrolyte abnormalities, and obstruction. If there is a headache I would be concerned about something going on in the brain such as increased pressure or infection at the surgery site. Would need more info such as time of vomiting, constant?, relation to meds?, involves blood? fever? able to tolerate any oral intake? headache? other neurological symptoms? And certainly it could be due to narcotic withdrawal. In addition to telling your PCP, you should tell her neurosurgeon so that he can decide whether further neurological workup is necessary such as diagnostic imaging or a neuro exam to make sure everything is ok in the brain and at the op site. Good luck.
Jessica