He needs a vet. That is the only thing you can (need to) do. They can't handle things well at that age and shouldn't have a cold but is more likely an infection or aspiration, is the pup nursing from Dam or being bottle fed though could happen in either case, just more likely if someone inexperienced is bottle feeding or something and is a common mistake. If that is aspiration pneumonia, a small particle was inhaled somehow into the lung, the reaction is to start filling with fluid and they will essentially slowly drown. That may not be it but is a possibility until you do know what the problem is. The only thing known now is that there is something wrong and the pup needs to see a vet today. Hope that baby is okay, good luck.
Its normal for puppies to have a cold. All you have to do is keep an eye on them for further un-natural behavior, if it worsens I do suggest a vet =)