For the last week my stool is dark and like sand. i have been very tired and gaining weight. everything i eat makes me nauseous. i have pain ?

Maybe melena?: "Melena" is passage of stools stained dark by with denatured blood. As we established in prior healthtap answers, all dark stool is not melena. Your doctor, or even an over-the-counter test that you can purchase, can check to see if your dark stool contains blood. False positive results can occur based on diet & stool additives. Nausea w/ dark stool however raises suspicion 4 stomach inflammation.