Im a 29/f & i wake up daily w/heavy sinus cngstn+headache. i take allegra (fexofenadine) daily for allergies. dont take any other meds. how do i avoid the headache?

Saline irrigation: If antihistamines are not helping, you may want to try a neti pot (saline irrigation). If this doesn't help, you may need to have an otolaryngoloist (ENT) take a look with an endoscope (look from inside) to exclude polyps or other functional causes of blockage.

May not be allergies: Sinus congestion and headaches although commonly due to underlying allergies may also be due to other causes. Also, otc antihistamines, like allegra, (fexofenadine) only control mild allergies and even then in only about 30% of people. You may have more severe allergies which have triggered the sinus complaints.See a board-ceritifed allergist for allergy testing and evaluation.