After having rt sided chest pain, a cxr was normal but ct scan showed rul apical infiltrate or fibrosis.do u have any guess as to what this means?

Depends: Doctors usually do not interpret ct's by themselves. We use all of the clinical information available to us to decide what a finding like the one you describe might mean. Depending on the clinical situation, a 5 CM opacity may be something quite benign to other more serious problems. A conversation with your doctor may help to enlighten you on what this is, and how best to pursue it.

Depends: Could be pneumonia, or infected blebs/bullae from emphysema, or cancer ... Ct scan can see more details than chest x-ray.

Possible pneumonia: Pneumonia is a possibility if you also have symptoms of an infection, such as fever and elevated white blood cell count. If not, and if the findings on the ct are stable over time, then this may represent chronic fribrotic changes from a prior inflammatory-infectious process.