It is possible that the blood in your stool is due to hemorrhoids or an external anal fissure, even without constipation. If the blood was bright red and has decreased significantly, it may be less concerning. However, it is important to monitor closely, and if the bleeding reappears, it is recommended to consult a doctor for further investigations to determine the cause of the bleeding. It may also be necessary to follow up on your thyroid hormone levels, but this is not directly related to the bleeding.