Problem(s) with Digestive System - Hard to Pinpoint the Cause(s)

Hi, for the past year of 2009, I have had about five times of near black feces - once was entirely black, the other four times were really dark brown, They seem to happen during times of stress, or incidents. The first time was when I put off eating for about a half-day, then ate a really big meal. The other times I think were when my toenail had been nearly uplifted and bleeding - dark stool not related to it directly, but to the pain and nervousness? The entirely black stool had happened about 3 and a half months ago. The other times seemed to happen closer in time and more frequent. One week ago, I ate nearly half a watermelon in the night, and the morning I had red stool. And another thing --- one that happens relatively frequently compared to the five time dark feces --- is that my stool comes out of me very quickly when I'm at the toilet, as if all in one strand, and I don't have control over how fast they come out -- and when they do reach the toilet, they become fluffy and broken apart, instead of retaining their solid form - they seem to be very soft or "perhaps" moist feces.
Thanks for any help in advance!  

[michael107]

Oh, and I doubt it is an ulcer because I don't have any weight loss, no loss of apetite, no vomiting.