I would invest in a Vicks humidifier, the one where you can put in a vapo stick into it. When my 2 year old has been stuffy or a small cough starts to develop, we run the humdifier at night while she sleeps and helps her sleep plus helps keep things loose. Moisture is a good thing to the nose & throat especially when the heat comes on in the winter and things dry out.
Also, have him gargle luke warm water with salt & honey. Works great on a sore throat.