My kitten won't meow or play...HELP PLEASE! :(?

Our 6 week old kitten had a really bad cold about a week and a half ago, but thankfully has gotten much better and is eating good. Everything in him seems normal except he no longer seems to meow and isn't even being playful. Ex When we first got him he would meow here and there, and he loved playing with the yarn ball....but now- nothing and this is after he had the cold. Could there be something else wrong with him?? He opens his mouth as if he was to meow but nothing comes out....I throw the yarn ball around him and he seems to completely ignore it :/ Has anyone had a similar experience, and if so how is the kitten doing now?