I also thought that I was really intolerant of sulfites, as most red wine gives me a headache directly, but it doesn't seem to be just that...

One way I noticed this was that my boss's favorite beer is Breznak, and so when he gave me a can as my first drink after-work, I got immediately headached, despite that it should have pretty low levels of sulfites. And then I made the connection a couple weeks later when the same thing happened. So the third time he wanted to hang after work, I took some macro lagers with me (Norrlands Guld), and I drank several without problems.

I can even drink a ton of vodka and not have a headache the next day... but if you give me a half glass of red wine or many different kinds of beer, I immediately get the worst headaches. I wish I knew why.