When I read about your headache I got reminded of my first flush. I had a killing pain in my head (can't remember if it was my sinuses too) but after 3-4 months flushing every 2 weeks I found out that all my allergies were gone.
Since childhood I always had sinus and earproblems.
Someone told me that like ear itching and sinus pain could be allergies.
My 1st flush is now about 10 years ago.