Lower Back Pain, Stomach Pain. Painkillers Ineffective

Hi for the last 3 weeks I have had lower back that doesn t go away even with painkillers. 4 days ago I started with very bad stomach pain, not cramps more like a constant gnawing pain that won t go away. It can last all day and no particular food sets it off it just seems that whatever I eat gives me this pain and it can last all day. I cannot sleep at night, I don t have wind, diarrhea , constipation or hearburn and I go to the toilet regulary every day although my stools seem to be different each time. It makes no difference to the pain if I am sitting, lying or standing up and it doesn t go away if I press on the area. Any idea what this can be.