It's actually not rare, Phony90. Iron deficiency is common among women in their childbearing years (because of our periods). And as you said, it's also common in vegans, women who drink (alcohol strips vitamins from your system) and anyone on acid blockers or antacids.
I got it in my 20s during a few of my heavier periods - not badly, but I would look a little pale and occasionally feel a little fluttery and dizzy. And it happens a lot to me now that I'm on Prilosec. Even with eating beef, I have to take major iron supplements or I become anemic very quickly.
But yes, it can also be caused by things like caffeine, too much exercise, anxiety, hormones and dehydration. Megan - it won't hurt you to take one iron supplement. I find when my symptoms are due to iron deficiency, one supplement fixes them almost immediately. So it's worth a try, along with hydration and charting the symptoms for a month.