For the last three weeks now my stool texture and color has changed . stool seems to not be well formed and soft and dark ?

Need to see a doctor: Soft stools which are dark (assuming by dark you mean more on the black side than brown), can be sue to bleeding in the upper intestinal track (stomach). Change in diet and other conditions can do this. Be sure to see your doctor.

Check with your Dr.: Stool can naturally change color and texture depending on whether you've had changes in our diet recently. However, small amounts of blood in the stool can turn your stool black. If this is a persistent problem, see your doctor for an evaluation. He or she may order a stool guaiac test to determine if there are microscopic amounts of blood in the stool.

Positive or negative: If you have changed your diet for the better, eating more whole foods, veges, legumes, whole grains and fruits, then the changes are a reward for a better diet. If the stool is very dark - black, odorous and loose, then you may be bleeding slowly from your gut/stomach area. A change in meds such as using Aspirin or nsaids may cause slight bleeding. Different foods also affect bowel function.