HELP my rat is twitching?

Okay so hes young but not a baby and we got him at a feed store so he is inbreed and most likely not very healthy. He hasnt shown any signs of illness except sneezing (could be reseratory problem) and he started twitching yesterday evening. When he sneezes it goes way but then it comes back in a few seconds. His muscles seem like they are tensing up around his chest. Sometimes when he does iit he makes noises in his mouth like he is chewing something but he isnt and the noises are loud for a mouse. We are gettng him a freind today but we are freeking out! please help! By the way we only got him last week.......HELP!!!! sorry for spelling mistakes im typin fast and PLEASE answer soon! thanks!