Hello courtneycooper, Constipation and abdominal pain at your age can be due to Irritable Bowel Syndrome or IBS . This is a condition associated with not only movements or contraction of the intestines but also excess sensitivity to distension of the bowel. This is related to certain harmone called serotonin. Condition is very common in western civilization. Aggravated by dietary factors, such as not enough fiber intake. Acid reflux is a separate issue. Lower back pains and blood in the stool is of concern. Although this may be related to straining and presence of small hemorrhoids at your age certain inflammatory conditions of the bowel can occur. These include Ulcerative Colitis and also Crohn s Colitis. The first one can affect part or all of the lining of the colon or the large bowel. The latter can affect any part of the entire digestive tract although more common , the small intestine. Colonoscopy is nothing to be scared about. It is done by trained specialists and done under safe sedation. I would encourage you to follow through. Wish you well.