Left Side Back Pain Under Ribs Since 15 Months

I have left back pain under ribs for over 15 months. Checked CT scans, MR , Ultrasound , X-ray , no problems have been found except gallstone which I know I have had for more than 20 years, but the left back pain under ribs started 15 months ago and therefore I ruled out the cause by gallstone. I have done blood tests and found QuantiFeron TB Gold positive, but no symptoms have been found on any X-ray and CT scans. I have seen many doctors, but none of them can tell me the exact cause. The pain is more like a inside hidden pain. When change positions like going to toilet, a quick sharp pain in larger area may come, but if I adjust my body slowly, the pain may not show up and can not be found any more. Occasionally after I eat, the back pain is magically gone for 2 or 3 hours. After that, the pain comes back again. When I take rest, I feel better. After a long sleep, I feel great without pain for the first 20 minutes or so, after that the pain comes back again.