While the medication you took, Acenac MR (which contains the pain reliever aceclofenac), can sometimes irritate the stomach lining, a short course taken two months ago is unlikely to be the direct cause of your current symptoms. However, your symptoms?especially the very dark stools, chest burning, and heaviness?require prompt medical attention. Dark stools can sometimes indicate bleeding in the digestive tract, and chest discomfort always warrants a professional evaluation. Please consult a doctor or visit an urgent care clinic soon so they can safely evaluate you and help you feel much better.