Welcome, Generally, pain in the back with constipation makes one consider that some stool may still be present. A doctor can tell if you are impacted with an x-ray and then you will need a better cleansing than what the laxatives provided you. I know you think you have gastritis but diagnosis should come from your doctor as you may think you have one thing but may have something completely different. With constipation please focus on adequate fiber, particularly water soluble, in an amount of 25 grams per day combined with adequate fluid. Increase fiber slowly or you will get gassy. Your stools will be hard without adequate fluid so assure that you drink 10 glasses of water per day, especially while increasing fiber. Instead of laxatives try a few prunes daily to get nutritious fiber and a laxative effect. Gastritis involves inflammation of the stomach. There are many causes but h.pylori is one of the infectious agents responsible and the etiology of the gastritis should be assessed by your doctor if indeed such a diagnosis exists. The treatment for gastritis depends on the cause. So, I must know that you have it and the reason for it to give you an idea of what to eat and what foods might aggravate your situation. Gastritis can also be worsened by some medications. B12, iron and calcium adequacy should be assessed if you do have gastritis. Please write back after you have seen your physician and have a diagnosis and some tests have been run to determine cause for your problems. Best wishes, Kathryn Shattler, MS,RDN