Trace of blood in urine only after bowel movement. Otherwise very clear every time I urinnate. I had a case of hemorrhoid but why blood in urine?

Prob not related. Blood in the urine may come from many sources most of which are not related to the rectum or anus. In the absence of any history of prior pelvic surgery radiation cancer or other benign diseases, any blood in urine which doesn't resolve should be evaluated by a healthcare professional.