It seems likely that you were experiencing a type of gastro-intestinal infection. In this case, a CT-scan is not the proper diagnostic tool. Microbiological examinations of the feces are more useful. At this time, however, you report no vomiting or diarrhea... I doesn't seem as if you will need further diagnostic procedures. Discomfort can pass spontaneously. Neither penicillin nor any other antibiotic are used for treating viral infections. Diet and a supplement of water salts are the most important actions for treating intestinal infections.