Hi there,
I have been reading down the whole thread and What I do recommend is to NOT use any medication to get down. This is a recipie for disaster. It could work yes I agree, but it could also work and stop working down there and cause an increased pressure to build up in the inner ear on the way up. So not you are down and cant come up.... or at least without blowing out your eardrum or worse a round window in the ear.
The suggestion about the widening of the sinus is the best idea I think, but your problem may be a very narrow eustation tube joining the back of your throat to your ear. Another thing I have seen in the past is the more diving you do the more it opens. But that means diving 2-3 times a week with the occasional 7 days in a row type thing. The ears are an area you dont want to put too much pressure on. Another thing I see offshore is divers equalise about every .5 of a foot if they have bad ears.
Have you ever had problems coming up?
Hope this helps and good luck with it