What could cause headaches for two weeks straight?

Too many to count!: Everything from eyestrain to stress, neck problems, upper back problems, rib problems, tumors, high blood pressure and on & on. To get a better answer, you should see your doctor. They should take a thorough history, do a thorough physical exam, including an osteopathic hands-on exam (which can find the causes of headaches missed by most other means), maybe lab tests to determine the root cause.