I saved a feeder baby 2 days ago and he is 3 wks old. He is very sick though with an upper respiratory infection. That night I started him on doxy so he's been on it for 2 days. But he still sounds really sick and he's been sneezing constantly for the last hour. He can't stop. What can I do to help him? I'm afraid I'll lose him cuz he's so small and young. Also should I add amoxicillin to his treatment?