Why do my rats keeping getting URIs?

Question
QUESTION: I have 2 boys and 2 girls. My little guy keeps getting URIs. I had him on bayatril and then I switched the vet because she refused to help me and the new vet lithium on amoxicillin for 5 days. I use fleece and wash it no fragrant detergent. I make my own food for them which is puffed wheat cereal dried fruit I try to give them fresh whenever I can. Sunflower seeds unsalted. I wash their cages out twice a day with white vinager or baking soda. I even stopped smoking even though I smoke outside because I was afraid the smoke on my clothes was causing it. I am so stressed and bout to cry cause I just want him too feel better what am I doing wrong?

ANSWER: Hey Patricia,
Honestly it sounds like your doing everything right. Do you keep them at a normal room temperature (71f) (21c)? Do you keep it like that? Is there a draft in your room where you keep them? Do you let them play on your clothes that you smoke in?
Other wise it sounds like your doing everything right.
Emma
If you want to answer my questions then feel free to ask or if you want to ask more questions don't hesitate!

---------- FOLLOW-UP ----------

QUESTION: I havea door that leads too the attic that may cause some sort of problem and since the weather has been warmer we have had the heat off with windows open and if it cold at night we turn on the heat which can dry the house out

Answer
Hi,
Yes that might be the problem, dust and draft, you don't have to do special care to the WHOLE house but if it's cold or warm give them special attention:
Cold House:
Extra blankets/towels
Maybe a towel over the cage to keep the heat in.

Hot House:
I've heard of people who put fruit in ice and give it to them as a special treat.
Basically try to give them cold thing subtract the extra blankets and such give them (If possible) a colder room.
Emma
Hope it helps!