What Causes Diarrhea, Left-sided Abdominal Pain, Nausea And Intestinal Gas?

Hello. I have been experiencing diarrhea for 9 weeks now. I have also been experiencing a pain in my left side as well as nausea and increased gas. I have been to my doctor several times now. She ran multiple blood tests and stool tests. The stool samples all came back normal (no bacterial infection, no celiacs), but the blood tests revealed that I have hypothyroidism and thyroiditis that were unrelated to my digestive issues. It became so bad that I lost approximately 12 lbs. at one point. I have changed my diet to include more fiber, bland white meat, vegetables and fruits in small increments, and brown or wheat carbs (rice, bread, etc). The diet change has made the diarrhea and nausea more manageable (primarily in the mornings), but the pain in my left side has gotten worse. It is now tender and painful to touch. I should also mention that I am a relatively healthy female of 25 years and am not pregnant.