Having occasional perineal pain extending from urethra to rectum .
Can be proctitis or urethritis.
Hello and thanks for using "Ask a Doctor" service for your query,
Possibly it could be proctitis. Proctitis is inflammation of the lining of the rectum.Rectum is inflamed due to bacterial invasion. On taking antibiotics these bacterias are killed so you feel relieved. Whenever Stool passes through the rectum on its way out of the body it compresses the inflamed area causing pain.
Go for stool and urine microscopy test
Proctoscopic examination of rectal canal to be done by MD.
Whether to go for colonoscopy or not would be decided by results of test.
Urine test would reflect if its urethritis or not.
Hope i was helpful,