I am experiencing abdominal pain, diarrhea, tender abdomen. i have had stool tests done to rule out all basic stuff, fecal fat test, blood work, ultrasound which showed cholelithiasis, enlarged spleen (14.3cm) , and fatty liver. surgeon not worried.

Fatty liver to start: Distinguish fatty liver (steatosis) from fatty liver with abnormal liver tests (steatohepatitis). Best to start with a weight loss diet based on calorie and fat restriction, avoid alcohol, control diabetes & cholesterol (if present). Your doctor will likely want to monitor your labwork and imaging, & consider all diseases that can promote steatosis.

Many possibilities: There are many possible causes for your symptoms. The most helpful clues will come from a very detailed interview by a knowledgeable physician, preferably a gastroenterologist. Shooting first with lots of tests and skipping the questions usually wastes a lot of money and often results in chasing lots of dead ends. If careful history and directed testing are reassuring, then IBS is the most likely.