Tumors of the world, unite!

I've gotten a headache every afternoon this week at work. Three theories:

1. Caffeine addiction (they go away when I get a soda)
2. Stress
3. Brain tumor

I'm leaning more toward the first two, since I don't seem to get headaches on my days off. Of course, maybe it belongs to the Brain Tumors' Union, and therefore does not have to work weekends and evenings...