If the regular daily dose of allegra (fexofenadine) is not enough is it better to take 2 allegra (fexofenadine) or take another medicine?

Depends: What for? If rhinitis, then you need to see an Allergist to better determine the cause of symptoms (specific allergens, non-allergic triggers, structural probems) to better target the problem with alternative meds. If for chronic hives, then higher doses of antihistamine are often employed (but again, would recommend seeing an Allergist before proceding). No benefit in alternating antihistamine