Talk to Gastroenterologist on Any One Suggestion And Investigation

I have consulted several doctors so far, but no one has been able to give me a clear diagnosis or explain the exact cause of my pain. I experience severe pain in the upper central part of my abdomen (epigastric area). The pain can last for 10–11 hours, and even medicines/tablets do not provide significant relief. The pain sometimes radiates to my back. I would really like to know what could be causing this type of prolonged pain. Could it be related to the gallbladder/gallstones, stomach or duodenal ulcer, pancreas, gastritis, intestinal problems, or something else? Please guide me about what tests or investigations I should have to find the actual cause