If you have constipated bowels, this could be due to a fissure or hemorrhoids which bleed while passing stool. In case of a fissure, you get pain while passing stool. Red-colored blood indicates fresh bleeding. Pregnancy
increases the blood flow to the pelvic organs and also the pressure effect of the uterus
enhances the effect. You should see that there is no constipation
and the stool passed is soft. You may use stool softeners. You can use local applications as advised by your doctor after an examination to localize the cause. Good luck.