This is exactly what I am thinking. I know children who have has RSV and they are on no medication. I have never heard of children having to take medications for that long when there was no damage or immune disorder. There is a reason why the common cold is called common. We are all going to get them.
Unless there was excessive damage to his vitals, there is no reason at all to keep him on medication. There is only a certain amount of time before the drugs will build up in his system and cause worse probelms. Who knows, you may even find that the phlem will decrease once he is off the medications.
My kids can have running noses for weeks on end. It's normal, and my kids don't even go to day care. Kids just have that. Maybe changing daycare locations would be a good idea too...if he is picking up that many colds then possibly they aren't observing the cleanliest practices over there. I know there is only so much you can control but then again...
From your original post I had thought of him as a sickly child. It seems like you have obsessive doctors indeed who are only out to pad their wallets and the ones of the drug industry.
I think the second opinion is a great idea!