Bad headache for almost 3 weeks?

Alright, im a 15 yr old girl... so ive had this really bad headache for just about 3 weeks, its constant, from the moment i wake up to the moment i fall asleep, ive woken up from it a few times too. when i have a headache i take a tylonal and it goes away.. with this.. im taking 2 tylonal and 2 ibruprofen every 4 hours.. and it doesnt help very much, it even doesnt help at all most of the time. the pain is in the lower back of my head. mostly to the left, at times it feels like someones stabbing me with a knife there. i drink water very often, and j havent changed my diet at all in the past 3 to 4 weeks. ive already gone to the doctors and they said if it gets worse or meds arent working to come back,,, that was a wek ago. and it has gotten worse and meds are NOT working. i come to think is a tension headache.. although im starting to think its not. im not trying to think of the worst. any answers or solutions to this? sorry for all the reading! thanks tons! -Emily