It started when my brother forced me to listen to one of his self-help CD's from Tony Robbins about the acid/alkaline diet (http://www.alkalinephdiet.com/anthony-robbins-alkaline-diet/). Mostly I view that stuff with a huge amount of skepticism, but my stomach will vouch for this one. As long as I have a veggie shake or a couple salads each day I'm able to safely drink coffee and alcohol, and occasionally eat pizza and other spicy food.
Those days I was pulling all-nighters every week or so, sleeping 4-5 hours on nights where I actually went to bed, ate complete crap (typical university student), and hadn't done any sort of exercise other than walking to-and-from class for a solid 12 months. Yes, I was drinking 3-6 cups of coffee and/or energy drinks a day, but it was when I fixed all of the other stuff (mainly sleeping & eating better) that I started to not feel like death every day.
I've had a few issues over the last year or so and I'm only just making the link back to an acidic diet (diet coke, spicy food and chocolate being the main ones!)