I have allergies but can't take allegra (fexofenadine) cause it makes me feel really drugged. Is it ok for me to just half of it every morning?

Better option. You could but it will probably be less effective. I would consider trying an alternative antihistamine. Zyrtec or Claritin are OTC or Xyzal (levocetirizine) is prescription. You may also want to consider a nose spray or even allergy shots (see an Allergist).