What would cause a 1 year old to start coughing only at night?

How is his breathing? Is it heavy? Has he been breathing from his mouth? Could be his tonsils...my son started doing that also. I got him checked by the doctor and she told me his tonsils are enlarged but hes still too young to have them removed. I don't know for sure if thats what your son has but i would see a doctor and get him checked out