a blocked nose and cough at 6 months is so heartbreaking to watch because they can't even tell you how uncomfortable they feel. Since it has been going on for a while and the cough is new, it might be good to bring him to see the PD just to be safe, so they can check if his chest is clear. In the meantime, keeping his head slightly elevated during sleep and using a saline nasal spray to help loosen the mucus can give him a little relief. Hang in there, you are doing great by looking out for him.