I am a 27 year old female, 5'6" and about 250 with no medical problems. Within the last 2 weeks I have got real serious about losing weight and have started increasing my water intake and watching more of what I eat. It was fine the first week and a half but within the last 2 days, I suddenly started having stomach cramps, and diarrhea. At first I contributed it to my increase in fiber, just "clearing everything out", but starting yesterday I noticed the diarrhea is now really dark, almost black and kind of flaky. There is no blood on the toilet paper when I wipe so I don't think it is blood making it dark. The cramping will come on suddenly and only last a few minutes but immediately afterwards, I need to go to the restroom. I am also feeling hot and cold at the same time and have had a few instances of dizziness. I've only had few bouts of nausea but my appetite is pretty much none existent the last day or so. What could be causing this?