Thanks for choosing health care magic for posting your query.
I have gone through your question in detail and I can understand what you are going through.
Yes tender head can be due to flu
and it occurs as the flu causes release of various inflammatory mediators which can cause these tender heads.
Your two main concerns about the headache and the mucus can be controlled only after controlling the infection. The same can be done after doing a culture and sensitivity testing of the mucus and ascertaining which antibiotic will be useful and then starting the specific antibiotic.
Hope I am able to answer your concerns.
If you have any further query, I would be glad to help you.
In future if you wish to contact me directly, you can use the below mentioned link:
Wish you good health,
Dr. Srikanth Reddy M.D.