Possible TBI

When I was 15, I went to my doctor about my constant headache, and he prescribed me Tylenol and nothing else. 1 Tylenol pill significantly relieved my pain for 8 hours (bad headache to none). Now I'm 22 years old where I take 1 650 mg Tylenol pill, and it only lasted 2 hours of slight relief (very bad headache to slightly bad headache). How long should I make a diary of Tylenol usage before I go to my doctor for a MRI or CT scan or x-ray?