Talk to Gastroenterologist on Chronic Diarrhea

I have been experiencing with chronic bowel problems for about 3 years. Initially, I had daily diarrhea with greasy/fatty stools (occasionally watery), abdominal cramps,bloating, occasional nausea, weight loss, weakness,whole body cramps and concern for malabsorption. Fatty foods consistently worsened my symptoms, while milk/dairy triggered diarrhea and nausea. A low-fat diet reduced the severity but never resolved diarrhea.It seemed to be like Steatorrhea. Over the past few months, my symptoms have changed. I still have daily diarrhea, but I now also experience constipation. Sometimes constipation replaces diarrhea, and sometimes loose stools despite feeling constipated. Stool appearance and color fluctuate, and stools are not always greasy anymore. Over these years,I have tried anti-diarrheal medicines (Metodine, Entamizole, n-flore), probiotics, herbs, and diet changes with temporary relief or fluctuations in the condition. My abdominal ultrasound was normal. Could this be IBS, SIBO, lactose intolerance, pancreatic insufficiency, bile acid malabsorption,dysbiosis or any another GI disorder? Which tests would you recommend for an accurate diagnosis so I can start medication?