Worsening of shortness of breath, with no typical infiltrate on x-ray and no fever does not sound like pneumonia. A “nodular density” is usually not considered to be a sign of acute pneumonia. The worsening shortness of breath, without an obvious explanation for it is worrisome. Despite the negative scan, again raises the question of blood clots to the lung, also called pulmonary emboli, which can occur without any sign of clot formation in the deep veins of the legs. In addition, not all clots to the lungs originate in the legs and not all clots to the lungs are blood clots. Also, such scans can sometimes be falsely negative.
If your shortness of breath has gotten progressively worse when you receive this response, you should return to your doctor or the emergency room (ER) to report this and request that they consider repeating the scan, and ordering a D-dimer determination.
Good luck.