I have been suffering with a severe headache for around 6 weeks now. how can this be normal?

It is not normal: Most people have a headache at some time, such as from colds and flus, lack of sleep, too much driving, long hours on the computer, stress at work, etc... Several over-the-counter options include Tylenol (acetaminophen), Motrin, Aleve, Excedrin Migraine, and their generic brands. A "severe" headache or one with other worrisome symptoms should be examined by a doctor, such as at the ER.