Black stools could be caused by something serious I think you need to see your Dr as soon as possible , a few years ago I was given some Turbanafine tablets ( I think that's how you spell it ) for a fungal nail infection and my stools turned black and visiting the loo more often , I saw a different Dr who told me to stop taking the meds and it cleared up , I have since found out that particular med can attack your liver hence the black stools so I was lucky to stop when I did .