Constant splitting headache and deteriorating mental function?

For the past couple of months I have had an almost constant, persistent splitting, overwhelming headache. it seems to be getting worse day after day, and I've begun to slowly lose my cognitive abilities, in that it will take me hours to complete a homework ignment that used to take 30 minutes tops, and I cant remember any information and am incapable of giving more than one or two word answers to any question, let alone have the ability to spark up a conversation of my own. my grades are slowly slipping because i cant concentrate during my cles, and even when i try I simply forget the words and knowlege minutes after it is spoken. I am also wracked with a consuming fatigue that envelopes my entire body and keeps me from accomplishing anything. I dont know whats wrong with me, and ive had an MRI, been to an ENT and have been seeing a psychologist for months now. Any help or hope of relief would be a godsend. thank you.