Headaches and difficulty concentrating

About last december, I started getting very frequent headaches, which got worse. I ignored the symptoms thinking that they were related to a poor diet or lack of sleep or anxiety.
However now, my symptoms have slightly changed and I'm sicker than I thought I was.
Everyday, no matter how much sleep I get, whether I have a cup of coffee, I feel tired, sleepy and find it very hard to concentrate on my studies. I also get the feeling you get if you haven't slept all night or slept for an hour or so..and feel slightly dizzy.
I have intense pressure in my head sometimes and feel like I have a bruise in my brain. Its a similar feeling to pressing on a bruise on your skin, however this is in my brain. All I really feel like doing is resting, and have a hard time reading, studying etc.
I have seen a doctor, however they don't know whats wrong with me even after a physical and blood work.
I was tested for anemia, hypothyroidism, vitamin b12 and k deficieny and diabetes..all results came back negative.
The symptoms are only getting worse. What could I possibly have?