My husband doctor has him taking a z pack and amox-clav 875mg and benadryl (diphenhydramine). he has a huge headache and wants to take an 800 mg ibuprofen. can he ?

Yes, if/ Headache: If he is not allergic and has no bleeding, kidney, or liver problems, yes, he can. Does he have a sinus infection or is the headache so bad it could be something worse like meningitis, encephalitis, spontaneous hemorrhage...? Does he have fever and cold symptoms? Does he have sputum production or facial pain? He can also rinse out his sinuses with sterile saline drops/spray to help.