Hi, a few nights ago, the night of Sat. 16th actually, I was minding my own bussiness talking with my little brother then I felt a alot of pain around my stomache area, which made me drop to my knees. I thought it was because I had to go poo. I thought nothing of it, but then I went and it was black. Yesterday and today, it is still black and watery/runny...even though I do plan on telling my parents today and make an appointment with a doctor, I need to know if this could be cause by an ulcer or something like that or something else.

Edit: I have a bump under my left armpit too that seems to have grown in size...