Hello! Thank you for the query. The most common reasons of constipation are bad diet (low fiber and mineral water intake), chronic intestines infection, IBS, medicines (ca-blockers, antidepressants), hypothyroidism, colon cancer. As you have had colonoscopy, colon cancer is ruled out. So all other mentioned reasons should be considered. Blood in stool if present on the surface of it, is most likely caused by hemorrhoids. Hemorrhoids direct reason is constipation. I suggest you to start with diet improvement. Please increase fiber rich products, mineral water intake. Physical activity should be increased (it greatly stimulates intestines to work). You should also start probiotic intake. If it wont help, you should have stool test, stool culture test, thyroid tests. Ask your doctor about Rifaximine (for chronic infection) treatment. Hope this will help. Regards.