WebMD Symptom Checker helps you find the most common medical conditions indicated by the symptoms Constipation, Difficulty starting urine stream, Feeling. Infections. Infections of the urethra or bladder, such as urinary tract infections (UTI), can cause swelling or inflammation that compress the urethra and block urine flow. Constipation. A hard stool in the rectum can push against the bladder and urethra, causing the urethra to be pinched shut.