Which antihistamine is safe for a 2 week old infant for allergy ?

None: there no antihistamine approved for babies below six months

NOT SAFE: It is NOT safe to give antihistamines to infants. Nasal congestion is common in newborns; NOT caused by Allergy; a periodic sneeze/cough usually helps to clear mucous. Infant saline drops w/ bulb syringe can be used to assist w/ nasal clearing. Place1-2 drops of saline in each nostril followed by gentle suctioning as needed. See doctor now for 2 week baby check-up if you have not already done so.

None: None that I am aware of. I am not sure he has an allergy either at 2 weeks of age. He may instead just have a cold. I would just use a gentle nasal saline spray and use a suction device like Nosefrida. My wife uses it on our 3 year-old. Use a cool mist humidifier too. And, have him see his pediatrician if no improvement. Most drugs used in infants starts at 2 years of age.

NONE !!!!: The first months are troubled by narrow nasal passages & exposure to dust, fragrences, smoke & other irritants.Baby tries to flush these out of the nose with mucous but this often ends as congestion & produces rattling with breathing. The best rx is washing out the nose with saline & suctioning the remainder. Eliminate irritants from babies environment & this will happen less.