Hello and welcome to HealthCentral!
While Nancy is quite right that we can't diagnose, I wanted to add a bit to what she said.
This headache could be a reaminder of the flu, but it could also be something else entirely. I really don't have much of an idea of what it is, but it IS important that unexplained headaches be checked out, so please call your doctor, if you haven't already.
As much as I'd love to be able to help you with an answer to your question, I really cannot. What is needed is an accurate diagnosis and the only person who can do that is a doctor who can review your and your family's medical history, discuss your symptoms with you, and conduct a complete examination. Nobody can diagnose via the Internet it just isn't safe.
Please contact your doctor and I hope you are feeling better soon.