Stomach is really hard and staying that way and has been for about 3 weeks now what could this be?

Lots of things: A hard, distended abdomen suggests gastroparesis (a slow stomach) or dysmotility of the small or large intestine. Distension is often reported by irritable bowel syndrome patients who exhibit no structural pathology. Partial or complete obstruction of the bowel can cause distenstion. Accumulation of ascites fluid (benign or malignant causes), pregnancy, organ enlargement, herniation are others.