my puppy had a cold last week. he just had a runny nose and a funny sneeze. didn't take him to the vet though...did call. vet said dogs get colds like humans. just had to make sure his potty trips outside were short and we had to keep his lil but warm....now....he's as good as new.
Take him to the vet. :-) Dogs, like humans, sometimes need medication to get over these things and feel better while they recover. If it turns out to be a virus, you don't want to risk a secondary bacterial infection that will need antibiotics - just like people. And just like some human patients, a simple cold can develop into bronchitis or pneumonia, which I'm sure you don't want to risk.