The pain you described and where you're having it sounds like an ulcer. You should go to your doctor and get checked for on because they can cure them now with antibiotics. I did the same thing you did for a while. I had a lot of stomach pain (and yes, the pepto bismol is notorious for causing black colored and strange stools. The green can just mean that it went through your colon quickly.) and i just used to treat it with TONS of tums and pepto bismol. I did more damage to my stomach doing that, and it turned out that my stomach just produces too much acid and i was on pills for it for a while. Don't worry about your pains! The dark stool could also be caused from an ulcer. If you see black in the stool, it could be digested blood. Go to your doc!!! My dad had an ulcer, and he had the same pains as you.
the color of your stools is probably caused by the pepto or tums, etc.