I have a 10 wk old kitten that the vet says has pneumonia. She prescribed doxicycline .01ml once daily. That was a week ago. He doesn`t seem to be getting better. Does anyone know how long before his breathing and rattling gets better? She said he would have to be on it for 21 days. I just don`t want to be jumping the gun thinking this should clear up too soon. Thanks.