HI, thanks for using healthcare magic
Headache can have various causes. As you mentioned , headache can occur in viral illnesses such as the flu.
Other causes of headache would be migraines, tension headache
, sinus headache
, cluster headache
, due to head trauma
, due to lesions or blood in the brain.
Most cases of headaches
are due to migraines or tension headaches.
It is always advisable that if a person is experiencing a headache which feels like the worse they have ever experienced that they should visit their doctor for an evaluation.
It may be a virus such as the flu that is making you feel unwell but it is bes to check with your doctor.
I hope this helps