I feel your pain! Your story sounds alot like mine. I'm 47 years old, suffering from headaches for the last 22 years. The last 2.5 years have been chronic. Lots of doctors including neurologists and endocronologists and they can't find anything. Most don't even try. I've done alot of my own research especially in the last 2.5 years since I haven't been able to do much else. I finally figured out just recently. You've hit the nail on the head....HISTAMINE OVERLOAD! Please do some research on histamine intolerance. Try a low histamine diet for at least 3 weeks. NO CHEESE, TOMATOES, CHOCOLATE, RED WINE, SPINACH, STRAWBERRIES, ETC. Try an Anti-histamine (ie. Zyrtec, Claritin, Benadryl) until the headaches are gone. I also think I have Candida but haven't been tested. I do believe it has something to do with the inability of the body to process histamine. GOOD LUCK.
It is very unlikely that food allergy or yeast overgrowth is the cause of your symptoms. Also it’s very unlikely that further diagnostic studies will reveal a cause. I assume that your neurologist is an expert on the causes of headache "chronic pressure around eyes and forehead" and has ruled out migraine variants and other types of headaches. Also I assume that all eye diseases, including those that could arise outside the orbit and press on your eyes, with increased pressure either in or around the eyes, have been ruled out.
If so, your best bet might be to seek therapy that could enable you to live better with your illness, to better tolerate the chronic pressure, and get on with your life, much as people with chronic pain are able to do. This might require psychotherapy to address the "mental fog-out-of-it feeling, sometimes referred to as depersonalization with or without a trial of other psychotropic medicines.
Good luck.