John,
I do not know if I can solve your problem but I can definitely understand it. I have always had chronic sinus problems and while usually able to clear my ears OK, a few times the sinus pain has been intense. Going slowly, ascending a bit, etc, all help but the last time I must have broken a blood vessel in the sinus and was snorting/spitting blood (lots) for days. My doctor is not a diver but also has similar problems and he says the key is to get the sinus cavities/passages to drain properly. To achieve that he recommended using an expectorant (Robitussin) and a decongestant, all of which cause drainage - not an antihistamine which dries up the secretions and adds to the problem. The Robitussin (expectorant) seems to work and I now carry it with me whenever I travel or dive.
Another thought which I just got from a freediving forum is to get some Papaya extract pills from a health food store. Stick the pill between cheek and gum about 15-30 minutes before diving and it is supposed to open up both estacheon tubes and sinus passages. I have not tried this yet but it is (theoretically) cheap and harmless so intend to.
Best of luck, Cliff