M.R.
My daughter had a runny nose for two months with clear discharge and the day that her top teeth broke through it stopped. So I wouldn't worry too much about it. Especially if you haven't given him nuts, milk, meat or other things that may lead you to think it is allergy related.
I did take my daughter in, and they said not to worry about it unless the runny nose is accompanied by a high fever (some of that is normal with teething too), a rash or diarrhea.