Talk to Gastroenterologist on Stomach Issue And Motion

My mother has motion from 3 weeks not loose like water but always in loose form and in black color .she take wverything ors ,yougurt ,no roti no salan ,she take liquid diet we visit 3 doctors in our area they give antibiotics she take all course but no relief in loose motions .its almost 3 weeks now what should we do doctors plz help me