My 3month old has a cough. when should i worry? he's exclusively breastfed, is eating well and has no fever. sometimes has nasal congestion but we suck it out with saline and the nose frida device

Doctor can check: Three months is pretty young. Babies can easily catch colds from other people. If there is just a runny nose, without much fussiness, without any high fever, without other worrisome symptoms, sometimes parents may leave the nose alone. If there is mucus in the cough and mild wheezing, or if breathing much faster than usual, a doctor might diagnose a bronchiolitis lung infection.

Persistent cough: If the cough is associated with fever,distress, poor feeding, or is persistent, please see your pediatrician.

Basics: If the kid feeds vigorously & retains it's normal activity level things are likely fine. If the feeding falls off, the kid seems to struggle to feed or breathe after nasal suction things are moving in the direction where an evaluation soon is needed. Sometimes this is just reaction to airborne irritants but it could be RSV or other worrisome problem.