You have had a pretty comprehensive evaluation for your symptoms. The abdominal/pelvic CT scan would rule out many of the major causes.
Prostatitis can still be considered. Further evaluation with a prostatic massage and subsequent analysis of the prostatic fluid can be considered. A transrectal ultrasound can be considered as well to rule out a prostate abscess. There are cases of prostatitis that may require several months of antibiotic therapy.
If the symptoms continue, more extensive imaging can be considered. This can include an MRI of the affected area.
These options can be discussed with your personal physician.
Followup with your personal physician is essential.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.