I awoke to cramping, went to bathroom and found lightish black-dark green stool is it due to school stress,not eating well for two week, birth control?

Stress/diet: Most likely your symptoms are due to school stress and/or something you ate. Your birth control is unlikely to affect the color of your stool. Some people can develop an "irritable bowel" during times of stress, and this can cause cramping, constipation and/or diarrhea, try to avoid or reduce caffeine, and increase the fiber in your diet. Probiotics may also help relieve your cramping.