hello I read your question and understand your concern I would like to ask that * are you taking iron supplements/iron injections for your pregnancy? * is there any abdominal cramps along with diarrhoea? * any episode of vomiting? * you are felling your baby movements ? in my opinion first thing is if you are taking iron supplements which is the must thing during pregnancy and at this 26 weeks than that black stool are due to that iron supplements, so I would like to suggest that stop taking those supplements first, and take plenty of fluids so not get dehydrated which will definitely not good for you and the baby as well and take semisolid diet and go to your obstetrician as early as possible to have check with her I hope my answer will satisfy you good luck & tc