4 month old has runny nose and sounds very stuffed up. what should i do?

Nasal saline: The use of liberal amounts (think garden hose) of nasal saline can help thin out thickened secretions & allow their removal with suction or by draining back into the stomach.This can also remove dust particles or other aggravating agents that make baby stuffy.

Usually give it time: If last few days only likely viral uri, a cold. If more chronic check with baby's doc. Do not use decongestants in young children, antihistamines do little for colds. Saltwater nasal spray might help.