K.L.
He may very well have a slight allergy to WHO knows what: dust, mold, pet hair, WHATEVER. See if you can get a referral to an allergist in your medical group and see if they will see your son. Even if they cannot treat him with allergy medicine, there is infants benadryll and other antihistamines that are safe for your little one to take. I know more than one child that has suffered from nasal allergies in infancy, its just a matter of finding the right doctor that wont blow you off - and NO, it is NOT normal for your baby to always have a stuffy nose all the time unless one of his siblings is getting and keeping him sick with the sniffles.
Since it says you have 4 children, that may be the problem. CHildren that attend school are covered in germs and bring them home - and since your baby hasnt had time for his immune system to completely develop, he might just merely have the same stuffy nose all the time because of the germs the kids bring home. I suggest having them wash their hands as SOON as they step in the door from school, and then use antibacteral hand stuff on their hands.