The description you have provided sounds like you are suffering from acute indigestion. This could be a reason why you are having so many problems all together. The first thing you should do is to take care of your acidity. Start drinking buttermilk as much as you can. Make thin buttermilk with a tablespoon of fresh unflavored yogurt in a glass of cold water and whip well. Add a pinch of rock salt to this and drink. Try to drink this at least thrice a day. This should help to fight your acidity to a large extent. The next thing you must do is to eat properly and at proper times. This will also help to control your bowel movements properly and will help you out tremendously.
As far as black stools are concerned, you must be aware that this could signal blood in your stools. Only a doctor will be able to tell you what is wrong with you in as much as that you are bleeding from within. So you should consult a doctor, who will in all probability make you undergo a battery of tests to determine what the exact problem is. A medical examination could also reveal whether you have piles or not.
answered by G M