I had a similar experience once. I was bawling like a baby I was in so much pain. My doctor diagnosed sinusitis and recommended Afrin and Tylenol Sinus (she also gave me an antibiotic scrip as a secondary measure). The next time I flew, a few days later, I was absolutely fine.

I am no doctor, I have no medical training, but the fact that you say the pain was very localized, near your nose, and the onset during the pressure change, definitely sounds to me like a sinus issue. I seem to recall WebMD had some useful information.

Best of luck, I hope you get a solution, quick!