Nodules on the lung are pretty common, i believe around 30% of the population. Very few of those are cancerous. It could be mucous, something you inhaled, or as the result of a previous infection. Its a waiting game and going back in 3 months for a CT is all you can do. I have the same thing going on, only they found 10 on my lungs, whereas 3 years previous i had none. They are having me wait 6 months. Good luck.