Hello There,
You might be suffering by 'Gastroenteritis ' or Food poisoning. Some times, stomach infections create much acidity and indigestion as a starting symptoms, due to which patient feels headache. Treating physician may get misleaded by such symptoms and treat only Headache.
Next Steps
Again visit to same doctor and tell him/her about your current situation and newly progressed disease. Your doctor will definitely change his plan of treatment and you will feel better.