Don't discount a dental issue, either. I have had dental problems in the past that appeared as some of the above mentioned items, or masked themselves as something else entirely. Altitude can aggravate certain conditions. A few years ago I experienced a great deal of pressure in a molar while riding to altitude for a skydive in a Skyvan (unpressurized). At 15,000 I felt a big pop and the pain and pressure went away about as fast as it had come. I later learned that a dentist who had performed a root canal a few months before, had drilled through that tooth into the next, and had also left an air pocket. Something there failed at 15,000'.
You can test the headset issue by flying next time without a headset. If the pain doesn't recur, there's a good chance it's your headset.
Rather than go get a different headset and deal with the expense, try making yours more user friendly. I have been an advocate for some time of using the oregon aero upgrades on existing headsets. The wide headband does wonders for reducing or eliminating "hotspots" on your head. The temperfoam earseals mould to your head with exposure to body heat (but are rock hard in the winter until they get warmed up...put them over your leg to heat them before wearing them). They have other products, too, but the earseals and the headband are for comfort, and are worth it.
If you are wearing sunglasses, quality or not, the temple bar and earpiece may be causing your headache if used in conjunction with a headset. This occurs because of the relationship of the earpieces and the sunglasses, usually pressing against your ear or head. One soloution is to cut the ear pieces shorter and just tuck them in the front of the earseal on the headset. Another is to wear the glasses on an angle, with the earpieces on top of your headset. A third soloution is to get the small foam earseal wedges that make wearing glasses a lot easier (again, oregon aero). A fourth and the most obvious soloution is to stop wearing glasses.
My helmet causes a headache after a short time. It's a reasonably tight "custom" fit, but I find that readjusting it slightly every once in a while usually takes care of the problem. Same for headsets.
Often the worst point for a headset, especially a clamping passive headset, is your jaw. It can be made much worse with a lot of talking, or chewing gum. Something to think about.
It never hurts to carry a couple of tylenol along on the flight. If the headache becomes a problem, or may become a problem, then bag the flight and land. A headache distracts you, possibly more than you realize, and may limit your vision, attentiveness, and ability to pilot the airplane. In worse-case scenarios, your condition may even become debilitating. Not a good time to find out, when flying.
Above all, if your condition isn't easily rectified with the various suggestions you're received, seek medical attention. You may have a condition that warrants it, and generally such things are best not put off for long. Good luck!!
