Again, when do babies start producing saliva and begin coughing? I rem…

Again, when do babies start producing saliva and begin coughing? I remember my son had it around 2-3 months old. And now my daughter is looking like she's spitting up sometimes, like she's throwing up. She starts coughing 2-3 times a day. Or maybe there's milk left in her mouth? I'm writing about saliva because I still hear something "hissing" in her nose, but everything is clean during an examination, and we even tried to suck gently too, it's clean. The checkup was last week, probably won't come back. There are still two weeks until the workup.