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.
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.