Black stools are a sign of blood from higher up in the digestive system. But you have been taking
Pepto Bismol. The colour is due to the bismuth in this medication. Try drinking lots of water and having more roughage in your diet such as bran, porridge, raw carrots. Don't be scared of seeing a doctor, he is there to help. Ulcers are caused by stress but cured by milk of magnesia and an antibiotic to knock out the bacteria that thrive in the ulcer which are usually Campylobacter
pylori......And if you have been knocking back the alcohol please stop for a while.