Ouch :(
I would be interested to see your pH levels. That's the main reason I have problems with coffee is the acidity of it. As my body becomes more acidic, red blood cells are unable to carry as much oxygen. I live 2 miles above sea level now and have become more aware of this process.

I'm only too familiar with the dull headache. lol I try to keep my consumption low enough I don't get that anymore. Not always successful though. :)