does your baby cough after taking milk? I mean to say dairy milk....not formula or moms milk! if yes, then see a pediatric doctor and tell the doctor this observation. I feel if it's due to milk then he's allergic to milk. stop giving him anything of dairy. let doctr diagnose and see. my boys too faced similar problem. I had to stop everything of milk...
another reason could be if ur child's cot is close to a wall. nowadays due to water seepage, the walls have mould growing on them. these are little white things that look like cotton candy and grows on the wall. if u have it, it's causing him breathing problems. keep bed in center of room and not touching a wall. treat the wall growth as soon as possible