Very dark brown stool?

I noticed yesterday i had dark brown stool (i had oreos that day so i just assumed it was from that). But today when i went to the bathroom my stool was darker than last time. I am concerned but ibs runs in my mom's side of the family and im pretty sure i have ibs. I usually have a bowel movement once every 2 days or so. I think it us just constipation cause i don't drink much water nor do i eat much fiber. I never had a hard hit or blow to my abdomen and im a pretty lazy person. If my stool is really dark the next time i go to the bathroom im going to let my mom know who is a gastroenterologist.