I stopped drinking all forms of coffee in June, a few weeks before YAPC. I had started drinking more coffee than usual, and started getting headaches when I went back to my usual coffee drinking routine. My first guess was that I was going through caffeine withdrawl.
I started drinking coffee again this past week. I'm taking it slow, and limiting myself to the old standby: a tall americano a couple of times per week. Drinking one or two 16oz cups of drip coffee per day was probably my downfall, assuming that there really was some sort of "caffeine withdrawl" at work.
What finally convinced me that coffee wasn't the sole cause of my headaches? Part of it was that they didn't go away completely when I stopped (they did lessen in both intensity and frequency). Part of it was that I started seeing an allergist who prescribed Allegra. My prescription drug coverage is pretty bad at the moment, so I used it for a few days and stopped.
Headaches are a common side effect of using Allegra (either using it or going off it; my doctor wasn't too specific). I did get some pretty strong headaches after I started, and stronger ones when I stopped.
I'm still getting headaches, but it looks like coffee (rather, caffeine withdrawl) isn't the root cause.
Trouble is, most of the headaches I get aren't really bad enough to be worth bothering a doctor with. They're just a bit annoying.
I think that the next thing to do is try to get a better bed. I'm convinced that the remainder will go away when I sleep better and don't wake up with a cricked neck.
-Dom