What Causes Slight Pain On The Left Side Of Body?

Hi. I had a slight pain on the left side of my body, right around the kidney area. I thought it was a muscle strain, so I applied heat. That didn t seem to help, so I applied an ice pack. the results were the same. The pain got worst, so I then went to the emergency ward. They took blood and urine samples and gave me a cat-scan. What they thought were kidney stones were not because the test results came back negitive. They gave me pain killers, thinking it was just a muscle strain in that area. Well the pain killers didn t do much good and now the pain is more constent. It feels like it s right at the bottom of my left lung. I haven t had much of an appetite since then, so my bowel movements the last day or two have ben few. So earlier today I felt like I was ready for a bowel movement, but as I went I had to strain and the bowel itself was about 4 inches long, hard, stiff and resembled a nugget-filled candy bar. I ve never had a bowel movement like that before. Could this be a stomach related disorder?