I would try to find anothr doctor and get his/her opinion. Maybe a gastroentrologist would be the answer.
I wish I had a better answer, but, I am not sure. Funny as it may sound, it could also be misplaced vertabrae in your back,maybe they are pressing on nerves causing the pain and symptoms, I see a chiropractor for things like this, and it really helps.
I wish I had an answer for you, but I'm actually going through the exact same thing. The positive Murphy's Sign almost always means some sort of gallbladder issue. It could also be your liver or digestive system since they are so close in proximity. They have probably already ruled all these out, but you could try asking about:
-kidney stones
-IBS (Irritable Bowel Syndrome)
-liver problems
-kidney infection
I would stick to your gut. You know what the pain feels like. When my pain started, they tried having me do physical therapy for back pain even though I told them it wasn't that type of pain. Now I've had 10+ trips to urgent care and my primary care physician and they are just now telling me to see a urologist. It sounds pretty stupid, but you could try putting your symptoms in to the symptom-checker on WebMD... But it might end up just making you obsessed (like me)
Please keep posting when you find something out.
Best of luck, Emily