Hi doctor. i've had a on and off headache for about a week now. i sleep well and have always drank a lot of water. do you know what the problem is?

Needs examination: Cant tell you without further details. May be a tension headache/migraine which is common in younger people, however needs examination and urgently if severe, vomiting, feverish, visual changes, drowsy

Headache : Headache can be due to migraine, tension headache , infection etc . Examination and detailed history can help to differentiate them . If having light sensitivity , severe vomiting or weakness in arms or legs or rash and fever then see a doctor immediately otherwise book an appointment to see your GP .