I am not sure about the adenoids. but constant congestion could be numerous things from as simple as a cold, allergies to Reflux or aspiration.
My ds had the reflux and aspiration and I was told over and over that it was normal, lungs sounded clear etc until I got him to a specialist and they finally listened to what I was saying. The lungs are an amazing organ and can clear alot of things with out "sounding congested" but that doesn't mean that they are not in danger.
Like I said it could just be a baby runny nose for the winter, lots of times they can pick up one thing after another and it seems to last forever.
My best advice is to follow your gut! I learned that we know our babies better than anyone can...even doctors. They are not perfect and miss things often. Do some research online, educate yourself about the possibilities. There are lots of sites out there. And go to your ped armed with data. If he/she dismisses you go to another doctor, even a specialist.....we used a pulmonologist and gastroenterologist. If you feel there is something more to this then there may be....dont stop seeking advice until you are satisfied!