Talk to Gastroenterologist on Stomach Or Intestinal Dissorder

Assalamoalaikum. I have stomach pain since last 3 years. i experience severe pain before having an meal and mild pain after meal. And its going on with severe pain after passing stool. I have taken approximately all medications with every pain killers of stomach and my almost all test are negative such as ct scan abdomen,anti ttg,H-pylori,ultrasound. when i used to take medicine it results me bitterness but when i complete my medications it starts again with severe pain... kindly give some guidelines...