Too much caffeine is what's actually stressing you out
At the end of an episode of Scooby-Doo, the villain is unmasked, and it's always one of the dudes they met earlier in the episode (we're looking at you, Old Man Jenkins). Well, the same logic applies here, in the case of why you're so stressed out all the time: caffeine is the culprit, and it keeps duping us all again and again (just like Old Man Jenkins!). Now, a little caffeine is fine to wake you up in the morning, according to recent research conducted by Dr. Travis Bradberry and Johns Hopkins, but the reason you need more and more of it is because you're going through short-term withdrawal, and the occasional late-day cup of joe is snapping you back to normal working capacity.
The solution? Cutting back on coffee. It's tough for a lot of folks, say the researchers, but the lessons in the long run are myriad. Caffeine triggers the release of adrenaline, which makes you overreact to your coworkers taunting you about your fantasy football team's performance... and, y'know, other non-fantasy football-related things.
It also has a six-hour half-life, which means that it takes almost a full day to work its way out of your system -- so assuming that you sleep (try it, it's totally great), it's affecting your ability to fall asleep and stay that way. While a single cup of coffee may be good to help you wake up, more than that will make you want to chase down those meddling kids in no time.