I am a 36 yr old female who is taking nexium for GERD and or gastritis. Every so often I experience this burning sensation around my stomach and upper area back which may last for several days. My bowels have changed in size, the color is usually normal, but I do not see any blood nor mucus, and when I did have a bowel movement there is pressure near the rectum area. I have gotten a colonoscopy which was negative. What could this possibly be, and if it is associated with GERD could there be another medication than nexium that may work.