Do not concern. Rectal bleeding is typically caused by hemorrhoids, in which blood vessels are swollen in the rectal area. Hemorrhoids are relatively common during pregnancy, particularly in the last trimester and some weeks after giving birth. But there are more chances of this condition if you strain during a bowel movement, pass hard stools. Anal fissures are another cause of rectal bleeding. Painful cracks in the skin of the anus may be caused by passing hard stools as a result of constipation, which is common during pregnancy. But as you told that you do not strain at all when you poop, there are less chances of these conditions. However blood in your stool is never something to ignore, so you must consult your doctor and go through examination and some investigations to diagnose the exact cause. All the best and take care.