What Causes Severe Abdomen Pain That Radiates To The Lumbar Region?

I'm been living with a abdomen pain, treated with Ibuprofen and it passed. I went to the doctor, and he said the sintomatology indicate Gastritis or Peptic Ulcer, he gave me Omeprazol for 4 week until the upper endoscopy exam, and the pain reduced. I went do the endoscopy and the report was normal, unless the esofagic candidiase I (he gave me Ranitidin, 1 pill per 90 days and Fluconazol 1pill per 4 days). My HIV test was non reactive (in the same day).
Now my problem is: I still with the pain when a get off the bed, witch takes 4/5min, irradiate to lumbar region, it alleviates when i sit down. Help me, what is that?