I have had a constant mucus problem for well over a year, and I also gave up dairy completely for four months, but it made no difference whatsoever.
I then went down the route of having my mercury Amalgam
fillings removed and doing a three-month heavy metal chelation protocol (using a very effective product called Humet-R, as well as chlorella, l-glutathione, and milk thistle). I definitely felt better after this, though the mucus situation was by no means resolved.
I then did an anti-Candida regime (diet plus rotating three different antifungals - caprylic acid, Pau d'Arco and grapefruit seed extract, as well as garlic and MSM in case of parasites, and because MSM also helps to heal the intestinal wall if it has been penetrated by Candida).
I felt quite a bit better after all this lot, but still not totally right. I then started addressing the issue of adrenal fatigue, using vitamin C, Siberian Ginseng, Ashwagandha and Rhodiola. I have been doing this for two or three weeks and have already noticed a difference.
Interestingly, it was only once I started dealing with all of the above that I realised I had had pressure in my head for a long time and was starting to suffer from nausea (which I mistakenly took to be Candida die-off). I was then told by a doctor that I had labyrinthitis (inner ear imbalance) and chronic sinusitis (though, like you, I didn't have a runny nose or sneezing, just a foggy head and what I thought were tension headaches).
I started taking plantago (tincture) to clear the sinuses, but then I stumbled across a recommendation for the use of Vinpocetine for vertigo left over after killing off Candida and removing heavy metals. Well, it's either one huge coincidence or this stuff is fantastic. Within three days the vertigo was gone. I then developed the worst cold of my life - I NEVER GET COLDS! What seems to be happening now is that the whole lot is - gradually - clearing. It's as if I have had every cold that I should have had in the last three or four years but which was suppressed - all at once.
I am noticing less mucus, which is a huge relief, but will post an update if anyone has managed to read this far and is interested!