Hi, Ktbear. I sure don't have an amswer but I do have some questions and maybe a way to get an answer. What color were the walls before? Did you wash the walls before painting? Did you prime? With what? Do you have a smoker in the house or do you use candles often? What part of the country are you in?
My guess is that the painting prep was inadequate but one way to possibly find out for sure is to take a sample to the store where you bought the paint. And take the old cans, if you still have them. Most paint companies have labs that can try to analyze your problem. I don't always believe them but they might be able to offer some direction. Most paint problems do take a while to show up and, yes, I do keep paint cans around for a year or more in case of warrantee problems. And I have found that you get better paint and better problem resolution if you deal with an independent paint retailer than with any of the "Big Box" stores.
If you can answer the questions above, I'll sure try to give you some direction. Henry in MI