It is likely that you could have had the bleeding due to a fissure or tear in the anal area due to constipation
.The black stool
is due to the ingestion of iron tablets which is a natural consequence. Yet, you should definitely exclude the possibility of vaginal bleeding. So, please go ahead with the check up as planned. Meanwhile, take bed rest
and keep a watch on any vaginal discharge
, fetal movements and any abdominal tightening. Ask your doctor if you can take any laxative as well as any local application to make passing stool easier. Wish you safe motherhood.