If you are suffering from severe and chronic abdominal pain and bloating after meals, have excessive gas, or have large bulky stools that may have blood in them, you need to go to a doctor. While there are many causes for this set of symptoms including dysentery and Inflammatory Bowel Disease (which can only be treated with medications), it may be something called celiac sprue which is treated simply with a change in diet to a gluten free diet.
Celiac sprue is an allergic condition of the small bowel that causes inflammation and damage to the lining hindering absorption of nutrients. This is why you get the symptoms of malabsorption and intestinal damage (bleeding) described above. You may also have weight loss and suffer from dietary deficiencies like iron deficiency anemia and B12 deficiency neuropathies for example.
The substance that your body is allergic to turns out to be something called gluten that is a protein found in many of the grain products in a typical diet including wheat, rye, barley, etc. The bad thing is that this food product is found in so many things, the good thing is that the treatment for this condition is simple, change your diet. No meds...