CT scan results freaking me out. Please explain

I had a CT scan to rule out a pulmonary embolism because I've been having heart palpitations after abdominal surgery.  The incidental findings of the report stated the following:

"There are numerous lymph nodes in the mediastinum.   Some small subcentimeter mediastinal nodes of uncertain etiology"

The radiologist suggested follow-up in three months.  

I saw the ARNP at my doc's office today and she told me that this is common.  But I am still worried as I did not see the doctor and she did not seem to know what it all meant.  I am so worried about lung cancer.  I have been a light smoker for 25 years (less than 5 cigarettes per day for most of these years, but heavier for short periods of time when under stress).  I am 38 years old.  Can someone please tell me what this means?  

Thank you for taking the time to read my post.

[Connie 1]

light smoking is a risk for lung cancer, but subcentimeter mediastinal nodes means that there are lymph nodes smaller than 1 cm in your mediastinum which can be normal, but if you're not satisfied with the ARNP's explanation then you should ask questions until you're satisfied with the answers

[HeinrikMD]

Hi.
The report showed some lymph nodes. Likely they are reacting against something - whether the cause is benign or malignant is difficult to say.
In general lung cancers would show a mass in the lung itself, which would subsequently invade the mediastinal lymph nodes - if only the lymph nodes are showing up, and they are present on both sides- would make one think more of lymphoma rather than lung cancer.
It would be better to consult a doctor and look for any symptoms pertinent to the findings. It is possible that you may have a chronic infection in the lungs, other diseases affecting the immune system may have similar findings as well.
I see no harm in a second opinion.
Bear in mind though, that observation is a valid plan.
Stay positive.