@donasmrs-- It probably is a sinus pressure headache. Fluctuating air pressure during flights can definitely affect your sinuses. It can also affect your inner ear pressure so the headaches could be due to either one of these. The headache must go away when the pressure in your ears and sinuses level off again after a few days.
You can try using saline nasal spray and chewing gum on flights to prevent pressure from increasing in your ears and sinuses.