resperatory infection, allergies, or other

So i've had my rattie (soon to be ratties) for about a month now and he's still sneezing. it's not like a constant sneez type thing, there's hardly ever red porophyn (or however u spell that) around the eyes or nose. it's just that he sneezes every once in a while without a reason. sometimes they're fits for like 5-10 secs every 5,10, or 15 minutes, other times its fairly often. i haven't really found a pattern. he eats and drinks plenty and is quite the playster--always racing up my arm to my shoulder, then i pick him up and put him down and he does it again. i really don't want to take him to the vet cuz 1. i dont think he nos much about rats, and 2. i dont want to spend a lot of money if it's nothing big. thanks for helping in advance :wink:

ps: i've switched from aspen bedding to carefresh and now im trying to litter train him so that i can use cloth bedding.