Hi A.,
When our now 5 month old daughter was 2 weeks old, she had excess mucus & was experiencing some labored breathing but no other symptoms. I took her to the ER to be tested for RSV but that, FLU, bloodwork, xray for pneumonia were all negative. We've been dealing with excess mucus up until a few weeks ago...
Through lots of troubleshooting and misdiagnosis we've now determined that her excess mucus and sinus issues were all being caused by acid reflux. I'm not saying your son has acid reflux but knowing you said he has no other symptoms, I wanted to share our experience.
Here are some things you can be doing if you're not already doing them:
Keep him comfortable
Pat his back with a cupped hand on either side of his backbone to help break up mucus
Suction the mucus to help clear his airways
Eliminate dairy from your diet(if you are nursing) and his if he has a milk protein formula
Use a cool mist humidifier in his room
Keep him upright to help with draining; elivate his mattress (I usually sleep with mine on my chest at times like this)
Put some baby vicks behind his ears, on his chest and feet
If this is an ongoing thing, I would research acid reflux. I didn't believe our daughter had acid reflux and was extremely bothered when the ped prescribed zantac as the first course of action. After some research we know now that the acid reflux/GERD symptoms caused the excess mucus/cold like symptoms we were seeing at 2 weeks and the past couple months.
Best of luck to you,
Peace,
J.