The cause of this pain and pressure is not clear. If it involved the sinuses, it should have shown up on the sinus CT scan. It could be a vascular problem in the area or related to a deviated septum, both of which either your ENT or the CT should have identified. Without an examination, it is difficult to present more options.
hi i'll tell you what happened to me in c ase it might have some relevance to you. I had a problem with excessive amounts of mucous in my throat - post nasal drip, cronic cough etc. It turned out to be an allergy to corn and corn products like corn/maize flour etc. Before this was determined I tried a new breakfast cereal. I don't know what was in it but I know it gave me really bad headaches similar to what you describe. Didn't try the pressure equalisation trick though. It was like a migraine in that all I could do was lie on the floor and curl up like a baby. It was amusing to my wok colleagues at least, if not to me. The usual pain meds didn't do much. Eventually after 9 days in a row of this I happened to run out of the breakfast cereal and suddenly the headaches were gone and have not come back. They would come on about an hour after eating. I have heard of other people with corn allergy that have migraines too. Harly scientific but the pieces seem to fit in my case. I guess if you have excess mucous too (mine appeared to come from my sinues - had clear CT scan too) it could cause some blockage and pressure imbalance which could be cleared by equalising like a scuba diver as you describe.
Do you have excess mucous as well? Coughing (to expel mucous?)
good luck & I hope it turns out to be a simple answer.