I used to drink 2 litres of Pepsi every night. Always had bad headaches, turned out that it was caused by the caffeine in the pop. Stopped drinking the pop, not only did the headaches disappear, but I also lost some unwanted weight.
I had the same problem with drinking alcohol!! Whether it was beer or margaritas (which I love) or even wine. I would get a massive headache even after one beer. I could drink 5 margaritas with no problem but I would wake up later that night with a splitting headache and lose many hours of sleep. But it wasn't until I went on my low sugar, low carb diet that I found the culprit. For 50 years I thought is was the alcohol giving me the headache!! I was absolutely wrong!!! It was the additives in the beer, wine and margarita mix (carbs and sugar). Now I can drink all the alcohol I like with no headache. Crown Royal with a little diet coke (no sugar and no carbs) and NO HEADACHE!!
It's really amazing how you think you know everything only to find that you know nothing!!