pressure in head with brainfog

well...first a bit about me. I'm a 25 year old make. I have no history of any serious illnesses. I have bad sinus problems, though and that is about it. I have excess phlegm since i was 14 or 15...it hasn't really gotten worse...but its constant and every day. Now onto the real problem.....About 2 and a half years ago, I started not being able to think so clearly, and my memory because an issue. I guess its the fact that it is such a stark contrast to how I used to be. I still have a sense of humor, but before this started to was extremely quick witted, and would remember stupid little details of everything...had extreme focus on things and I guess put simply...My brain worked well lol. Now I am many times at a loss for words, and even simple things like a person's name won't click. I see them...and it doesn't enter my mind for a few seconds. These are even people that I see every couple days or so. I have a constant pressure in my head like something wants to push its way out of it ! Not a pounding headache or severe pain...but a dull, aching pain that seems sometimes to come from the side...but sometimes all around. I put things down and just seconds later forget where they are. I don't mean just like my keys occasionally...but EVERYTHING. I put down a piece of paper, walk away, and forget where it was. I look away, and forget what I was doing a second before. I am not exactly depressed...more like nervous and worried. My doctor ordered a CT scan to be done...and I did it, and it said it showed no signs of any growth in that area of the head. I'm still worried about it being a tumor though. I went to a psychiatrist and he said it could be anxiety. I've tried eating VERY healthy, lots of fruits, veggies, garlic, walnuts, omega 3s, etc...to no avail. I've looked up things and found that it could be mercury or fluoride toxicity, even lyme disease (I've gotten tick bites about 10 years ago!). I want to get to the bottom of this but don't know what type of specialist to go to....as none of them seem to think its any big deal. They dismiss it as depression or anxiety. The only thing making me depressed is the fact that I don't know what is wrong. I just feel "not right"...I feel "off"...like there is a constant cloud over my brain...can't think clearly at all. Help