Drinking water is the first thing I try because headaches are often caused by a lack of water in your system. If that fails, ask yourself, "When did I last eat?" Being hungry is another reason for having a headache and/or nausea. Stress is number three and four is hereditary migraines. At least with myself.
drink water see if that helps.
You are either thinking to much or never heard of a thing called sleep.
There are many causes of headaches. Too many to make a guess without more information.
could be an allergy if there were not poisonous gases (exhaust for instance), or some emotional interaction with someone (a disagreement)