Nausea, vomiting, headaches, dizziness, fainting episodes. Negative pregnancy test. Causes for symptoms?

Hi,
The symptoms you have mentioned occurs in many situations.
You have already excluded pregnancy. I presume that your hemoglobin levels were normal too.
Other causes can include any of the following
a. Sinusitis
b. Stress
c. Low nutrition
d. Decreased sleep
e. Low or high blood sugar levels.
And many other disease conditions.

First thing to do is to get evaluated by a physician to rule out any serious conditions. You should also be evaluated for eye, ear, nose and throat disorders. After those examinations and required tests as prescribed by the physician, diagnosis and treatment would be easier.
Meanwhile, you can make small modifications in your lifestyle. Regular short exercises, proper food at regular times, drinking of plenty fluids and adequate sleep would all keep you fit and healthy. Meditation techniques can give you some de-stressing moments.
Hope I have answered your query. Please get back if you need any further assistance.

Regards