Does My Rat Have a U.R.I ?

My rat has always been a sneezer when he was seepy or if their was a change in the room (temp, Smell..) Hes been like this since i got him at 5 weeks old in May.. Im just worried because for the 2nd time he has a bit of porifarin on his noes.. bothe times is old just been there for a day then its gone and wont come back for a while, but each time its just tiny wet red dots at the very corner of his nose... i listend to him hes breathing sounds fine... and his eyes are clear and hes poops apear ine... does he have a URI or is it just the changes that bugg him? Im willing to take him to the vet I just dont want to if its just me being a worried momma and not a sick little rat