Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with your doctor.
Without the ability to examine you and obtain a history, I can not tell you what the exact cause of your symptoms is. However I will try to provide you with some useful information.
There are several causes of headaches. Headaches can be divided into
primaryPrimary amyloidosis
Primary biliary cirrhosis
Primary hyperparathyroidism
Primary insomnia
Primary lymphoma of the brain and secondary.
PrimaryPrimary amyloidosis
Primary biliary cirrhosis
Primary hyperparathyroidism
Primary insomnia
Primary lymphoma of the brain headache
disordersAdjustment disorder
Anorexia nervosa
Asperger syndrome
Autism
Autoimmune disorders
Bipolar disorder
Bipolar disorder
Bleeding disorders
Borderline personality disorder
Bulimia
Chronic motor tic disorder are headaches without a direct cause. These are diagnosed after secondary causes have been excluded. Secondary headache disorders are due to an underlying problem, there are many many causes but some include medication side effects, systemic illness, nervous system infection, tumors, bleeds in the brain or clots in the veins of the brain, and others.
Primary headache disorders are much more common than secondary ones. There are several primary headache disorders. For example migraines, which usually a pulsating throbbing one-sided pain with nausea and discomfort in bright lights that lasts several hours. These are often associated with changes in whether, as you describe or with light discomfort such as looking at a tv. Another possibility are tension type headaches, which may occur as a band in the front of the head, or in the back part of the head similar to what you describe. If your headache is in the back of the head associated with neck stiffness and pain, it may be your headache is related to neck strain or neck arthritis as well.
Without further information about your headache, it is difficult to provide you with adequate information. However, it is important for you to understand that if you have not experienced headaches in the past and you are now having new head pains, seeing a physician is a good idea, just to make sure there is nothing serious causing this pain. Imaging of the brain and sometimes then neck may be indicated depending on your exact symptoms, your physical examination, and other factors.
Thank you for this opportunity to answer your questions, I hope you find the information I have provided useful, good luck.