Pooing blood?

21weeks 5days pregnant and pooing blood all day? I woke up this morning went to the bathroom went poo and looked down it looked like my period I started freaking wiped realized it wasn't from my vag so I didn't worry much , so I went to the bathroom again and the same thing bloody poo,  then just now again , I have slight back pains and slight cramps in the front but that could be growing .. but is this normal ? Should I go to the er?! First time mom here. 
UPDATE: went to the ER, ended up in labour and delivery . Baby is fine and its internal hemerroids caused by the pregnancy and that's causing the bleeding - it IS common , and to use stool softeners and to eat more fiber .