Food, chemical, & inhalant reactions are the most common cause of headaches. Also, magnesium deficiency. Consider allergy testing. See Great Smokies Diagnostic Laboratory or other labs for testing. Avoid caffeine. Will need to gradually withdraw so as not to get withdrawal headaches. Rule out other medical causes.
Be sure to stay adequately hydrated. Please see Dr Slagle's Newsletter "Stay Hydrated,Summer Tips for more information.