Thanks for the further information.
A neck sprain is not likely to cause nausea; though neck stiffness and headache can be related. The headache can be related to nausea; and migraine is the commonest for both of these symptoms together. You can take an over the counter medication (do not need prescription) Excedrin migraine. If you are relieved, it would confirm it to be migraine. Please read the symptoms of the migraine in this resource;
There are two types of medications used for the treatment of migraine;
1) To abort the attack
2) To prevent the headache
Valproic acid, gabapentin
Calcium channel blockers
Beta-blockers, tricyclic antidepressants
There are dietary triggers known which should be avoided. Common triggers are
b) aged cheeses and meats,
c) wine and beer
d) citrus fruits.
Still an headache and nausea of one week duration should be evaluated by your doctor, especially if you have following risk factors;
1) stress and sedentary life style
2) peripheral vascular disease (claudication),
3) previous stroke,
4) heavy smoking,
5) high blood pressure,
7) high cholesterol, and
8) a family history of heart disease
9) over weight
Please feel free for your follow up questions.