What Causes Pressure And Stabbing Pain In The Lower Abdomen?

Hi, I ve been experiencing sharp, stinging, pressure, fullness, searing and burning pain in my left abdominal and left lower lumbar/thoracic portion of my back since March/April 2015. No doctor can inform me of the problem. It never goes away though the symptoms vary from severe to moderate. I am now starting to feel some pain in the lower right quadrant portion of my abdominal. So far it s been ruled out I am not pregnant, nor do I have endometriosis, diverticulitis, IBS. I ve also had CAT Scans, X-Rays, Vaginal Ultrasound and an MRI done (Nothing). Do you have any clues of what can be happening? Every Physician has sent me home.