Hi I have a question about black stools?

ok so I went to the ER the other day becasue I was having sbad stomach pains. I have been putting up with stomach problems for the last 5 months and have been to the doctor a number of times. I am on nexium for an ulcer and the ER doctor told me that they couldnt do anything for my cuase i just being in sever pain that you cant move is not an emergency. She said that i would have to wait till my scop in 3 weeks to find anything out...She also told me to try some pepto bismol......which i did as the doctor order and finish offa bottle in two day ( you can take up to 8 times a day) ....i was reading about it and pepto bismol makes ulcers bleed!!! So i have conocluded my doctor was not very smart about that.....but I am feeling a bit better however I have black stools and I know pepto can turn them black, but I am afraid that it also made my ulcer bleed and that is why they are black....idk...If it was bleeding would there be a lot of pain?? or is there a way I can tell if i am bleeding through an ulcer. I would go to the doctor but when they find out that i was taking pepto they will just dismiss it as that and not do any test.