Your . Your question does not include very much information. Have you injured your head or neck? The bottom portion of the back of the head is called the occiput. The cervical spine (bones in the neck) connect to the skull (the boney housing for the brain). A number of muscles are in this area. Strain or damage to these, could lead to pain. Some people tense the muscles in their neck and / or shoulders when they feel stressed which can also lead to pain at the back of the head.
Headaches . Headaches are so common that many physicians consider them to be "normal variants" (90% of people have at least one headache during any given year.) however, any time a person develops a persistent headache or has a significant change in their usual headache pattern, medical evaluation is warranted. Occipital headaches (headaches in the back of your head) could be due to a sinus infection, neck problems, or so-called tension headaches. I see you posted your question a week ago. If your headache is still present and you haven't sought medical attention yet, see your doctor. Good luck!