Believe me its not out of nowhere. I have suffered from headaches for years until I found out why I was getting them. As I don't know your lifestyle I will tell you what brings on my pain.
First of all sugar, toxins you know when you have a sugar rush well what goes up must come down same goes to you, Sugar bring you on a high and a low. Look out for E numbers you will find them in cheap sweets and certain foods. Some are natural some are the causes of headache. Research E number. I am a sugar addicted and Allergic to nearly all the E Numbers out there especially in sweets. I have recently stopped and feeling much better.
Stress can bring it on it sounds like you have a tension Headache. So Relax and drink some herbal tea.
Florescent lights you know those cheap factory lights which are in schools also can give give you a tension headache .
You could also be dehydrate. Do you ever get a stinging pain in your eyes?
I would recommend you keep a food diary and your mood for the day.
This is a great way of understanding your body. And can also tell you what sensitives you have with certain food. For example Chinese restaurants have GMO "genetically modified organism" added into so to make you eat more and more. If you are sensitive to GMO you will get a terrible headache.
Finally you could go and see a nutrients who will do allergy tests on you and will tell you which food to eat to stay healthy
Hope this helps
Where I live, told by a TCM professional, where headache can not be relieved by medication like Panadol, it is highly likely that free radical/early tumour be the cause (he is consulted for such treatment)